Endless "Syncing (X%, Y GiB)" on the untrusted device

Hello, Thanks for the awesome software! I’ve been using Syncthing for years and it has replaced Dropbox and all similar services for me. Great work!

The issue I’m having is related to sync with an untrusted device. Configuration is the following:

  1. Master. Raspberry 4, 4 GB RAM, external HDD. Local state ~260 GiB. Everything works perfectly. Running as systemd service, natively. Version: v1.17.0, Linux (32-bit ARM)
  2. Slave. Raspberry 4, 4 GB RAM, untrusted device, external HDD with enough space. Trying to sync roughly 150 GiB. Local state ~99 GiB. Running as systemd service, natively. Version: v1.17.0, Linux (32-bit ARM)

Both devices are connected locally (only for now, later will be in different locations).

The issue is that the untrusted device has been stuck with “Syncing (X%, Y GiB)” forever. So it has synced nicely about 100 GiB but not cannot proceed with the last 50 GiB.

In the untrusted device’s logs I don’t see anything fishy or fancy but there are many “syncthing: pull: generic error” errors. For example:

2021-06-07 17:02:03 Puller (folder "FOLDER" (mzrtx-itcu9), item "Q.syncthing-enc/GN/9FK0M64L7VRGULD7L9BSD66TQSO0QILEJGB83NAD6GVK3K8SM956D91FU0QQ0DE82E82P"): syncing: pull: generic error
2021-06-07 17:02:03 "FOLDER" (mzrtx-itcu9): Failed to sync 1 items
2021-06-07 17:02:03 Folder "FOLDER" (mzrtx-itcu9) isn't making sync progress - retrying in 1m0s.
2021-06-07 17:03:48 Device DEVICE_ID_HERE folder "FOLDER" (safgq-pwxsz) is delta index compatible, but seems out of sync with reality
2021-06-07 17:03:48 Device DEVICE_ID_HERE folder "FOLDER2" (swm4c-jltgd) is delta index compatible, but seems out of sync with reality
2021-06-07 17:03:48 Puller (folder "FOLDER" (os6me-gschk), item "S.syncthing-enc/IC/T8NTH3I2KTGE0HU38LIKUDVTBN68SGOLSP4962SMJ53JTTEBFRTC993RE4E036DUO5VBGU24N3INRRDDU99I7K79PS68NS2SKPRELGODO26FT6GKSI91J4PFTGVSGSIEH9V4AHL4DKC4U7P9K3OOTSRP4TUPJDJLM6V9LUI8J5EV6685GQAHDMATG"): syncing: pull: generic error
2021-06-07 17:03:48 Puller (folder "FOLDER" (os6me-gschk), item "J.syncthing-enc/PH/5BK65FQLSELEO5OSKH1VKEK446QJLCNMBDFJF5BED0BD8S2F3KLQ2MTEUH7JV5IV62V6RM8NHV0H54G9355NHUGI08U5PCUFG054JM9A9LK69VPOT2V9I3FQ9D5Q2CEF0KBGH1545KQ4LGOIS43T7M7IU1JCHHESR54UVNLR3J3MKACJ1LPMBFU1JEHNIRSJR08J0AQ8/NBOM8UCBO9OV0J4"): syncing: pull: connection closed
2021-06-07 17:03:48 "FOLDER" (os6me-gschk): Failed to sync 2 items
2021-06-07 17:03:48 Folder "FOLDER" (os6me-gschk) isn't making sync progress - retrying in 2m43s.

On the master device I see in logs:

2021-06-07 19:06:38 model@0x263ce00 Completion(UNTRUSTED_DEVICE_ID, "of6da-nya5f"): map[completion:96.08224059055777 globalBytes:30926199809 globalItems:36088 needBytes:1211614103 needDeletes:0 needItems:13272 sequence:128398]
...
2021-06-07 19:06:39 model@0x263ce00 REQ(in): UNTRUSTED_DEVICE_ID: "hshft-korrs" / "FOLDER/FILE_HERE" o=0 s=131072 t=false
...
2021-06-07 19:08:57 Index update (in): UNTRUSTED_DEVICE_ID / "of6da-nya5f": 90 files

The thing is that I’m not syncing big files. The folders in which the untrusted device has been stuck have normal small to big files.

I’m not sure what is the issue as it’s not very clear from the logs. Could someone please help to look into the right direction?

What state is the folder on the untrusted device in? Can you post screenshots from it.