A reset may be unnecessary as I think I may know what’s going on.
I just discovered this thread: Keypad won't change security mode "some devices need bypass"?
This is exactly what I was doing but I had the prompt volume set low so I did not hear the warning from the base station that the door sensor needs bypass confirmation.
So the problem isn’t that it auto-disarms, it’s that I’m not confirming the bypass and the system is not arming at the end of the leave delay.
I’ll test again and confirm if this solves it.
However, a notification to the app explaining “door sensor triggered, bypass required” would go a long way to avoiding this confusion!