It used to work very reliably for many years and I used it for pretty much everything (photos, ebooks, notes, Signal backups, …). However, last fall it simply stopped syncing (traffic at 0 B/s) in 90% of the cases, no matter the file size, even though my devices see each other and Syncthing recognizes that files are out of sync. I have already reset and reinstalled Syncthing various times – no idea what's going on.

My gut feeling says that it's the Android client[0], but I'll have to find the time to look into this more closely.

[0]: https://github.com/Catfriend1/syncthing-android

I've also encountered this periodically and the way I've gotten things back to normal was to 'reset database' in Syncthing-Fork's troubleshooting settings. Is that what you meant by reset?