Just a quick update. I have now upgraded all devices to v1.14.0 (self-compiled). I did have to reset the databases, etc., but right now everything is 100%* in sync.
I have also additionally enabled STTRACE=db,model,versioner on my main machine, which has tons of folders, so the log files will be massive, but I am running Syncthing with
syncthing -logfile=default -logflags=3 -log-max-old-files=9
so the logs should take only ~100 MB maximum. Hopefully, I will be able to spot the issue before the older logfiles are deleted. I’m now going to keep observing the situation and come back with some debug logs if the files get stuck in sync again.
* Except for https://forum.syncthing.net/t/folder-stuck-in-sync-and-non-matching-local-and-global-states/16431, but this is a non-issue really.