fellow #fairphone users:
since the last android update, my phone (FP4, Android v15) kinda regularly closes apps even when they're in use.
examples: music streaming, podcasts, etc, as well as Bluetooth connections.
no app timers are set up.
"manage app to save battery" is turned off for the affected apps.
[EDIT:
Turns out lots of people have that issue. Solutions so far: do not work for everyone, not to the same degree, not long-term.
This is fucked-up. 馃槪
Some suggestions in the replies.]