Client keeps disconnecting and stuck on Sync at 0%

Hi, me and my friend are trying to sync data but syncthing keeps disconnecting or stuck at sync files, we both run Windows 11 and Syncthing version 1.22.2, also this problem we got recently happened after he changed PC so maybe he is the problem.

I add the logs of both pc’s if someone can help us fix this problem.

Friend Logs.txt (61.4 KB) My Logs.txt (3.0 MB)

According to the log files there were some intermittent network connection issues, but the main problem is that there appears to be more than one instance of Syncthing running on your friend’s PC.

Your PC is receiving a connection attempt from device “IR74CUV” while your PC is reaching out to device “NS4HAIO”.

Your PC is receiving connections from an unknown device:

[VLEUW] 2022/12/30 12:18:22 INFO: Connection from IR74CUV-K77A3BT-XDZZV3Y-Z2WV2AP-66EOOHR-LVL4G2V-TLV3I6I-ASSFWQF at (relay-server) rejected: unknown device

How can I fix this? I don’t know from where the other connection is coming, I also checked if he had more than one instance running but there is just the one that we configured in the pianification utility.

I also have just his device connected to my syncthing.

I covered his name because he don’t want it to be shown.

Do you and your friend have any other devices also with Syncthing? (e.g., computers, phones, etc.)

First thing to check is that your PC and your friend’s PC know each other’s device ID.

According to the log files you posted, Syncthing on your PC has the ID “VLEUW6G” (it appears in the “This Device” panel).

Expand the “Remote Devices” panel on your PC, the device ID shown should match the one on your friend’s PC. And on your friend’s PC, your device ID should appear in his Syncthing’s “Remote Devices” panel.

Yes they are Matching I have his ID and he has Mine just as you said, we have just 1 connection so idk where i’m getting the other connection.

Extracting the device IDs from your log files shows that your friend’s PC is seeing only one remote device, yours (VLEUW6G), while your PC see’s two remote devices (IR74CUV, NS4HAIO). Which one is your friend’s?

On your friend’s PC, Syncthing’s log says:

[start] 2022/12/30 12:06:04 WARNING: Error opening database: The process cannot access the file because it is being used by another process. (is another instance of Syncthing running?)

The ID of my friend is IR74CU

Combining your friend’s device ID (IR74CU) and yours (VLEUW6G) in a text search of your log files, you’re sharing a Syncthing folder named “Mondi Core Keeper”, but the folder ID doesn’t match between each side:

[VLEUW] 2022/12/30 22:39:33 INFO: Adding folder "Mondi Core Keeper" (gul9d-dcphm)
[VLEUW] 2022/12/30 22:39:33 INFO: Ready to synchronize "Mondi Core Keeper" (gul9d-dcphm) (sendonly)
[VLEUW] 2022/12/30 22:39:33 INFO: Completed initial scan of sendonly folder "Mondi Core Keeper" (gul9d-dcphm)
[VLEUW] 2022/12/30 22:39:54 INFO: Device IR74CUV folder "Mondi Core Keeper" (gul9d-dcphm) has a new index ID (0x681F1AFADA98A131)
[VLEUW] 2022/12/30 22:41:03 INFO: Adding folder "Mondi Core Keeper" (4gqe2-5wshr)
[VLEUW] 2022/12/30 22:41:03 INFO: Ready to synchronize "Mondi Core Keeper" (4gqe2-5wshr) (sendonly)
[VLEUW] 2022/12/30 22:41:03 INFO: Completed initial scan of sendonly folder "Mondi Core Keeper" (4gqe2-5wshr)
[VLEUW] 2022/12/30 22:41:56 INFO: Device IR74CUV folder "Mondi Core Keeper" (4gqe2-5wshr) has a new index ID (0x42590FF46F9907BD)

Your friend’s PC uses the folder ID “gul9d-dcphm” while your PC uses “4gqe2-5wshr”. The folder ID must match, otherwise Syncthing treats them as different folders.

We’ll try tomorrow, thank you for your help, hope we can fix with this

No problem. Glad to help.

Hi, we redone the whole process and now it “works”, like it downloads and uploads file but every 2/3 seconds it disconnects and then restart, now the files are shared and work but there will need a lot of time for sharing like this, you know if there is some fix for this kind of problem?

If what I’m seeing in the log files you posted earlier still apply, Syncthing is relying on relay servers for both ends of the connection. There also appears to be some cases where the network connections are being dropped.

One of the reasons for passing thru relay servers is if Syncthing cannot find a way to directly connect to a peer. If either you or your friend configure a port forward, it will allow Syncthing to do so. See the Firewall Setup page for more details.

The firewall instructions unfortunately don’t say anything about Windows (note: I’ll have to add that sometime!) which is used here on both sides. However, you basically need to set the network to private (see and also allow Syncthing to access the network. The latter is usually done on the first run through a pop-up like this:



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