Stuck syncing/out of sync with disconnects

Hi, I have issues that Syncthing is taking ages to sync a few (though some large) files. The setup is a send only dir on one machine, receive only on the other.

For whatever reason I am getting disconnects between the clients. It might be related to my VPN disconnecting sometimes, but the clients are on local network. I’ve even disabled the relays etc. to just use local discovery.

It seems like Syncthing syncs couple of MBs/KBs, then looses connection, waits like hour or even more and then repeats.

Why is Synthing setting so large and seemingly random retry intervals (1h11m! couldn’t find a setting for it)?

Journal from the receiving client:

Sep 08 06:15:57 hostname wpa_supplicant[941]: wlp3s0: CTRL-EVENT-BEACON-LOSS
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Connection to ***redacted*** at 192.168.0.14:22000-192.168.0.13:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: read timeout
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Puller (folder "tohostname" (tmt8v-4qaq7), item "***redacted***"): syncing: no connected device has the required version of this file
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: "tohostname" (tmt8v-4qaq7): Failed to sync 9 items
Sep 08 06:26:20 hostname syncthing[11644]: [F4BHT] INFO: Folder "tohostname" (tmt8v-4qaq7) isn't making sync progress - retrying in 1h11m0s.
Sep 08 06:28:14 hostname wpa_supplicant[941]: wlp3s0: CTRL-EVENT-BEACON-LOSS

If possible, please add screenshots showing the Syncthing Web GUI on both sides. You can obfuscate any personal information, but please leave the version information visible.

Also, what operating systems are used here? Have you checked your firewall settings? If Windows is involved, the network needs to be set to “private” to allow direct connections, or otherwise Syncthing will be forced to rely on relays, which can be much slower. If they are disabled, as stated above, then Syncthing may not be able to connect at all.

Added screenshot from the receiving machine, both are Archlinux, same version of Syncthing. It looks the same on the sending machine, just the folder is not “Out of Sync”, but “Up to Date” and the receiving machine is listed there as “Syncing ([percentage and size])”.

You should get to the bottom of the disconnects, as that is most likely the cause. They should not happen under normal network conditions.

I agree, but it seems Syncthing isn’t recovery gracefully from disconnects, taking too long time. I think this message might be evidence of that:

syncthing[11644]: [F4BHT] INFO: Folder "tohostname" (tmt8v-4qaq7) isn't making sync progress - retrying in 1h11m0s.

Or does the message mean something else? How is this retry interval calculated? Is it configurable?

This message is just because the folder has been making no progress - which is impossible, because no devices serving the needed files are connected.

If the connection gets re-established, syncing immediatly resumes. New connections are attempted every 60 seconds, pretty much infinetly. As soon as your network (or the other device) is back up, they should reconnect a minute after.

As for the disconnects, it sounds a bit like some crappy WiFi network that collapses when under load - but that’s just a wild guess, could be anything.

1 Like

Ok, the weird thing is that the devices have been shown in the Synthing GUI as connected, with statuses as I mentioned (OoS/Syncing on receiving machine, UtD on sending) both with 0BPS transfers. I remember that I’ve been able to ping between the devices (now Syncthing started using IPv6 for some reason and I can’t ping the IPv6 addresses).

OK, I’ve found the issue. After restart of the sender machine it started working fine. I decided to do another test and transfer few GBs of data. Halfway the I got into what I think was the state I described in the first post. Ping between the devices stopped working (“Destination Host Unreachable”). Looking into the log journal on the sender device I see some kernel wifi driver issues (microcode errors on Intel wifi driver). After disconnecting the wifi, reconnecting Syncthing caught up almost immediately.

If I can give some suggestions it would be nice if Syncthing device & folder statuses were more clear and accurate at all times, perhaps doing some more diagnostics tooling in the background (I’d expect it to utilize ping at least).

Thanks for all the help diagnosing the issue and the work on Syncthing!

I think I’ve spoken too soon, now I’m at the same state as at the start, the devices are pinging to each other just fine. Just Synthing is stuck.

Including logs from the receiver device:

2021-09-11 03:25:32 Connection to HASHsender at 192.168.0.14:22000-192.168.0.13:41902/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: read timeout
2021-09-11 03:25:32 Puller (folder "toReceiver" (tmt8v-4qaq7), item "file1"): syncing: no connected device has the required version of this file
2021-09-11 03:25:32 Puller (folder "toReceiver" (tmt8v-4qaq7), item "file2"): syncing: no connected device has the required version of this file
2021-09-11 03:25:32 "toReceiver" (tmt8v-4qaq7): Failed to sync 2 items
2021-09-11 03:25:32 Folder "toReceiver" (tmt8v-4qaq7) isn't making sync progress - retrying in 37m43s.
2021-09-11 03:27:37 Connection to HASHanotherDevice at [anonymizedIPv6address%wlp3s0]:22000-[anonymizedIPv6address2%wlp3s0]:22000/tcp-server/TLS1.3-TLS_AES_128_GCM_SHA256 closed: read timeout
2021-09-11 03:30:23 Established secure connection to HASHsender at [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:23 Device HASHsender client is "syncthing v1.18.1" named "sender" at [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:42 Established secure connection to HASHsender at 192.168.0.14:22000-192.168.0.13:42656/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:42 Replacing old connection [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 with 192.168.0.14:22000-192.168.0.13:42656/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 for HASHsender
2021-09-11 03:30:42 Connection to HASHsender at [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: replacing connection
2021-09-11 03:30:42 Device HASHsender client is "syncthing v1.18.1" named "sender" at 192.168.0.14:22000-192.168.0.13:42656/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:52 Established secure connection to HASHsender at 192.168.0.14:22000-192.168.0.13:42664/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:52 Replacing old connection 192.168.0.14:22000-192.168.0.13:42656/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 with 192.168.0.14:22000-192.168.0.13:42664/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 for HASHsender
2021-09-11 03:30:52 Connection to HASHsender at 192.168.0.14:22000-192.168.0.13:42656/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: replacing connection
2021-09-11 03:30:52 Device HASHsender client is "syncthing v1.18.1" named "sender" at 192.168.0.14:22000-192.168.0.13:42664/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:31:13 Established secure connection to HASHsender at [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:31:13 Replacing old connection 192.168.0.14:22000-192.168.0.13:42664/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 with [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256 for HASHsender
2021-09-11 03:31:13 Connection to HASHsender at 192.168.0.14:22000-192.168.0.13:42664/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: reading length: read tcp 192.168.0.14:22000->192.168.0.13:42664: read: connection reset by peer
2021-09-11 03:31:13 Device HASHsender client is "syncthing v1.18.1" named "sender" at [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:31:13 Connected to already connected device HASHsender (existing: [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256 new: [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256)
2021-09-11 03:31:46 Established secure connection to HASHsender at 192.168.0.14:22000-192.168.0.13:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:31:46 Replacing old connection [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256 with 192.168.0.14:22000-192.168.0.13:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 for HASHsender
2021-09-11 03:31:46 Connection to HASHsender at [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256 closed: replacing connection
2021-09-11 03:31:46 Device HASHsender client is "syncthing v1.18.1" named "sender" at 192.168.0.14:22000-192.168.0.13:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:32:33 Established secure connection to HASHanotherDevice at [anonymizedIPv6address%wlp3s0]:22000-[anonymizedIPv6address2%wlp3s0]:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:32:33 Device HASHanotherDevice client is "syncthing v1.17.0" named "another Device" at [anonymizedIPv6address%wlp3s0]:22000-[anonymizedIPv6address2%wlp3s0]:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:35:23 Pausing HASHsender
2021-09-11 03:35:23 Connection to HASHsender at 192.168.0.14:22000-192.168.0.13:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: device is paused
2021-09-11 03:35:29 Listen (BEP/tcp): TLS handshake: EOF
2021-09-11 03:35:29 Connection from HASHsender at 192.168.0.13:22000 (tcp-server) rejected: device is paused
2021-09-11 03:35:34 Resuming HASHsender
2021-09-11 03:35:34 Established secure connection to HASHsender at 192.168.0.14:22000-192.168.0.13:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:35:34 Device HASHsender client is "syncthing v1.18.1" named "sender" at 192.168.0.14:22000-192.168.0.13:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:40:03 Connection to HASHanotherDevice at [anonymizedIPv6address%wlp3s0]:22000-[anonymizedIPv6address2%wlp3s0]:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256 closed: read timeout
2021-09-11 03:40:14 Established secure connection to HASHanotherDevice at [::]:22000-[anonymizedIPv6address2%wlp3s0]:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:40:14 Device HASHanotherDevice client is "syncthing v1.17.0" named "another Device" at [::]:22000-[anonymizedIPv6address2%wlp3s0]:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:42:34 Connection to HASHsender at 192.168.0.14:22000-192.168.0.13:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: closed by remote: device is paused
2021-09-11 03:42:49 Established secure connection to HASHsender at [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:42:49 Device HASHsender client is "syncthing v1.18.1" named "sender" at [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:42:54 Failed to exchange Hello messages with HASHsender at [::]:22000-192.168.0.13:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256: Application error 0x0: closing
2021-09-11 03:44:34 Established secure connection to HASHsender at 192.168.0.14:22000-192.168.0.13:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:44:34 Replacing old connection [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 with 192.168.0.14:22000-192.168.0.13:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 for HASHsender
2021-09-11 03:44:34 Connection to HASHsender at [::]:22000-192.168.0.13:22000/quic-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: replacing connection
2021-09-11 03:44:34 Device HASHsender client is "syncthing v1.18.1" named "sender" at 192.168.0.14:22000-192.168.0.13:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:44:36 Established secure connection to HASHanotherDevice at 192.168.0.14:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:44:36 Replacing old connection [::]:22000-[anonymizedIPv6address2%wlp3s0]:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256 with 192.168.0.14:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256 for HASHanotherDevice
2021-09-11 03:44:36 Connection to HASHanotherDevice at [::]:22000-[anonymizedIPv6address2%wlp3s0]:22000/quic-client/TLS1.3-TLS_AES_128_GCM_SHA256 closed: replacing connection
2021-09-11 03:44:36 Device HASHanotherDevice client is "syncthing v1.17.0" named "another Device" at 192.168.0.14:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256

sender device:

2021-09-11 03:25:32 Connection to HASHreceiver at 192.168.0.13:41902-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: read timeout
2021-09-11 03:30:23 Established secure connection to HASHreceiver at [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:23 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:42 Established secure connection to HASHreceiver at 192.168.0.13:42656-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:42 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at 192.168.0.13:42656-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:42 Connection to HASHreceiver at [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: reading length: Application error 0x0: closing
2021-09-11 03:30:52 Established secure connection to HASHreceiver at 192.168.0.13:42664-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:52 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at 192.168.0.13:42664-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:30:52 Connection to HASHreceiver at 192.168.0.13:42656-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: reading length: read tcp 192.168.0.13:42656->192.168.0.14:22000: read: connection reset by peer
2021-09-11 03:31:13 Established secure connection to HASHreceiver at [::]:22000-192.168.0.14:22000/quic-server/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:31:13 Replacing old connection 192.168.0.13:42664-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 with [::]:22000-192.168.0.14:22000/quic-server/TLS1.3-TLS_AES_128_GCM_SHA256 for HASHreceiver
2021-09-11 03:31:13 Connection to HASHreceiver at 192.168.0.13:42664-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: replacing connection
2021-09-11 03:31:13 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at [::]:22000-192.168.0.14:22000/quic-server/TLS1.3-TLS_AES_128_GCM_SHA256
2021-09-11 03:31:13 Connected to already connected device HASHreceiver (existing: [::]:22000-192.168.0.14:22000/quic-server/TLS1.3-TLS_AES_128_GCM_SHA256 new: [::]:22000-192.168.0.14:22000/quic-server/TLS1.3-TLS_AES_128_GCM_SHA256)
2021-09-11 03:31:46 Connection to HASHreceiver at [::]:22000-192.168.0.14:22000/quic-server/TLS1.3-TLS_AES_128_GCM_SHA256 closed: reading length: EOF
2021-09-11 03:31:46 Established secure connection to HASHreceiver at 192.168.0.13:22000-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:31:46 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at 192.168.0.13:22000-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:32:43 Established secure connection to HASHanotherDevice at 192.168.0.13:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:32:43 Device HASHanotherDevice client is "syncthing v1.17.0" named "another Device" at 192.168.0.13:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:35:23 Connection to HASHreceiver at 192.168.0.13:22000-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: reading length: read tcp 192.168.0.13:22000->192.168.0.14:22000: read: connection reset by peer
2021-09-11 03:35:29 Established secure connection to HASHreceiver at 192.168.0.13:22000-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:35:29 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at 192.168.0.13:22000-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:35:29 Connection to HASHreceiver at 192.168.0.13:22000-192.168.0.14:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: reading length: read tcp 192.168.0.13:22000->192.168.0.14:22000: read: connection reset by peer
2021-09-11 03:35:34 Established secure connection to HASHreceiver at 192.168.0.13:22000-192.168.0.14:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:35:34 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at 192.168.0.13:22000-192.168.0.14:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:40:13 Connection to HASHanotherDevice at 192.168.0.13:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: read timeout
2021-09-11 03:42:34 Pausing HASHreceiver
2021-09-11 03:42:34 Connection to HASHreceiver at 192.168.0.13:22000-192.168.0.14:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: device is paused
2021-09-11 03:42:39 Resuming HASHreceiver
2021-09-11 03:42:49 Established secure connection to HASHreceiver at [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:42:49 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:42:54 Connected to already connected device HASHreceiver (existing: [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 new: [::]:22000-192.168.0.14:22000/quic-server/TLS1.3-TLS_AES_128_GCM_SHA256)
2021-09-11 03:44:20 Established secure connection to HASHanotherDevice at 192.168.0.13:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:44:20 Device HASHanotherDevice client is "syncthing v1.17.0" named "another Device" at 192.168.0.13:22000-192.168.0.11:22000/tcp-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:44:34 Established secure connection to HASHreceiver at 192.168.0.13:22000-192.168.0.14:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256
2021-09-11 03:44:34 Replacing old connection [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 with 192.168.0.13:22000-192.168.0.14:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 for HASHreceiver
2021-09-11 03:44:34 Connection to HASHreceiver at [::]:22000-192.168.0.14:22000/quic-client/TLS1.3-TLS_CHACHA20_POLY1305_SHA256 closed: replacing connection
2021-09-11 03:44:34 Device HASHreceiver client is "syncthing v1.18.1" named "receiver" at 192.168.0.13:22000-192.168.0.14:22000/tcp-server/TLS1.3-TLS_CHACHA20_POLY1305_SHA256

Like I said during that time (since ~3:31) the devices were consistently pinging themselves. Syncthing was stuck as described in the first posts, pausing and resuming the devices in Syncthing didn’t help as far as I could tell (waited couple of minutes; anyway such manual intervention shouldn’t be necessary to recover gracefully).

This morning I found the files synced, so it eventually recovered, but it took too long. I think the issue might be Syncthing hanging on too long to invalid connections, it switching to IPv6 or something like that…

That’s IMHO a red flag. If the network is flaky all kind of weird things might happen.

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