Windows Desktop client "Changes in synchronized folders could not be tracked reliably"

Hello all
Could someone give me some hints/ideas how to troubleshoot the following issue on Winsows 10 desktop client 3.1.1? After upgrading from 2.6.5 to 3.1.1 the following error message is displayed after the start of the desktop client: " Changes in synchronized folders could not be tracked reliably" (in German: “Änderungen in synchronisierten Ordnern konnten nicht zuverlässig nachverfolgt werden”)
I’ve configured 3 folder synchronisations on the client what used to work very stable in the past. Now, after the upgrade, just one of it seems to have this issue. When I add a file to a synchronized folder it’s almost synched immediately to the server on two of those sync targets. But on one of those 3 it doesn’t work.
I haven’t tested in both directions and I didn’t wait for a long time yet.

I’ve deleted the faulty folder synchronisation on the desktop client and added it again. No success. I de- and reinstalled the desktop client (just in the Windows control panel, didn’t remove some files manually). The error still appears.

Ideas?

Some more details I should provide?

Thank you very much in advance for your help.

There you have a few points for troublehshooting and where to get the logfiles:
https://docs.nextcloud.com/desktop/3.0/troubleshooting.html

Because it was working before, it looks a bit like a regression which means this is a good candidate for a bug report. Logfiles are interesting, if you find any difference in the folders, I don’t know perhaps different file system on the client, or data from external storage. Or is it always the third one, try to add a forth one and a different as third one.

I’d take a look at the bug tracker: Issues · nextcloud/desktop · GitHub, regressions easily qualify for a bug report. Just make sure that there isn’t already a topic. Ideally you find a way and procedure to easily reproduce this problem. It can also help if others with similar problems share their configuration.

Thank you! I will try it soon. The computer is currently not accessible to me. I will post the updates/findings here.

OK, here are the results of my additional testing and some more information:

  • Removed the folder that is not synched automatically and added a new folder (completely new partnership). The message still appeared after restart of the desktop client but it was one of the other folders that isn’t synchronized then. Then I added the one again that I removed and it can synch now. So the folder or its contents is obviously not the problem.
  • Synched the folder to another PC and that worked too.
  • Activated the log with F12 and can’t see something special (like an error). The log is really big and I’m a bit lost because I don’t know what to look for.
  • 2-Way synch for all other folders are working fine
  • Within the folder that doesn’t synchronize I’ve added a testfile. All other files have the green tick but the new one hasn’t. So obviously it isn’t recognized by the sync client…
  • Copied the contents of the unsynchronizable folder to another place on the same HDD, then deleted the synch partnership and added it for the new folder where the contents are copied to. Still the same problem…

update follows…