got a warning that my phone ran out of space and I found the problem: syncthing-android filled its log file with endless repeats of:
[X2KPZ] WARNING: Listen (BEP/quic): Accepting connection: read udp [::]:22000: recvfrom: connection refused
since there are no timestamps I don’t know how fast it spammed this. At the first warning I did not notice that it was syncthing and just deleted some files (around 500MB) and after 2 hours I saw the warning again and found a log file with the size of 2GB, deleted it and it started growing again (only this line, nothing else), a reboot stopped it.
Another problem: syncthing should have been stopped at this moment since I set it to only run while charging and it was not charging at this moment.
Version: v1.3.1 for syncthing and syncthing-android