I use Android and I have faced with the same error.
I’ve also made a new vault in my Syncthing folder via the Android app. The vault was created. As synchronization happened, I opened it on my laptop. Then I copied all my notes from the old vault to this new vault. As synchronization happened again, I saw my notes in the new vault via the Android app.
But then I restarted the Android app and faced with the same error again.
UPD: the solution is here [Bug] % and # symbols in .md filenames causes "File not found" error and hang when loading vault