Syncthing is a free, open source tool to sync files between devices. It is available on Linux, Windows, MacOS and Android. Most of the time it just works. But sometimes you will get an "Out of Sync Items" error.
This problem often occurs when you haven't used a device for a while. Unfortunately, the interface does not provide any solutions to solve this issue. This is probably why the Syncthing forum is full of entries related to this problem. It becomes especially confusing, if the list of items contains no files. I guess that means that files were deleted.
Recently I got this problem again, but my usually solution, using --reset-deltas didn't work. So I had to dig
deeper. The log had an entry stating the affected folder "has mismatching index ID". Good to know, but I couldn't find
information on what to do.
The information I found was that Syncthing uses index databases. So I tried deleting all index data and it worked! So below are my solutions you can try to solve the "Out of Sync Items" problem.
I hope this information helps someone in the future. It would be nice, if there was an option in the Syncthing interface, that lets you select a device to force syncing from that device to the local device.
Solution 1
Shutdown Syncthing and restart Syncthing on the command line with:
syncthing --reset-deltas
Solution 2
Shutdown Syncthing and delete all index data by running the following on the command line (Linux):
rm ~/.config/syncthing/index-v0.14.0.db/*
The folder name may be different for you because of version number changes.
On Windows or Mac you could use the file manager to delete the files.
Restart Syncthing with:
syncthing