Simulator button presses terminate app

When starting my widget in simulator (e.g. fenix 6 Pro), the button presses no longer call the BehaviorDelegate functions (like  onPreviousPage), they just terminate the widget. The only button that still works, is the Start button calling onSelect. I set breakpoints on the first line of the onXXX function, they are not hit.

I did not change anything in the code and it worked before. Must be related to an update.

In general:
Most of the time when I develop Garmin Connect IQ apps I'm struggling with getting this general stuff to work. There are Eclipse crashes, simulator freezes, different behaviour of simulator and real devices, the above problem, and so on. It's not really fun to use that stuff. Android development for example works a lot better without that general problems.