OK so stock FP OS latest release.
There were some problems with the camera crashing earlier on, a couple of years back, but more recent problems have I think been imputed to the A15 generic memory management problems that were fixed in C.089.
It’s certainly worth opening a ticket with official Fairphone Support. I don’t remember seeing recently a problem similar to yours. This might be due to a faulty component. Warranty would presumably apply.
You could also try swapping in camera modules to test. Maybe contact a Fairphone angel if there’s one near you.
Sure. Developers are inconsistent 
In theory no app should crash but gracefully notify the problem …