One folder stuck syncing, others with same settings are not

Folder X is hosted on a Linux desktop machine (device A) and is shared with two android devices (B and C). Folder Y is also hosted on A and is shared with B and C with the same settings. Devices B and C are stuck syncing X at 99% and have been for a couple of weeks now, despite the contents of X changing several times since then. However, both B and C are syncing changes with Y just perfectly.

The difference is about 2.5 MBs that B and C won’t sync. Scanning on A finds all the changes in X just fine. Rescanning on B and C doesn’t seem to do anything, as the last scan time is showing a couple of weeks ago on both, although at different times because the devices are not used constantly.

All three versions of syncthing are now 1.14.0. Device A was running a slightly older version that I then updated in an attempt to fix this issue. There are no ignore patterns set up, folders exist on all three devices and sync was working perfectly as expected until about three weeks ago on device C, about a week and a half on device B. A, B, and C are all on the same home network. No folder settings were changed before the sync issues began. X and Y are not subfolders of each other.

I’m new to syncthing issues, it’s always just worked for me, so I’m unfamiliar with what information may be needed. I’ll provide whatever is necessary. Thank you all.

–chriscrutch

There should be a list of files/dirs which are not in sync. Please check if those are actually in sync (like manually checking file mod. time/size). And if there’s anything special about those files.

I tried removing the offending shared folder from syncthing, and the local versions from B and C, then re-creating the file share and starting fresh. The only difference now seems to be the number of files that still will not sync. The files are not physically on B and C (admittedly I only checked a random sample, however, there’s thousands of files out of sync now), and on A there doesn’t seem to be anything “odd” about them, although I also don’t exactly know what I’m looking for. The files on A don’t appear to be corrupted, machine A can open the files just fine.

–chriscrutch

If something is missing from a device (A) on multiple other device, the “problematic” device is likely that one. As in it somehow doesn’t send the info about those files to the others. For further debugging info, you can query GET /rest/db/file — Syncthing v1 documentation for one of the files on all devices. To try and fix it without knowing what the problem was, start Syncthing once with -reset-deltas on device A.