+1 on it being the alarm.
The tipover switch can also be looped at it's plug, eliminating it from the circuit.
The tipover switch is a simple sealed gravity switch, if it rattles, and is upright, it should be ok, lol.
But, even reading correctly, it can still be bad, and be like a relay that tests well, but fails under load.
It is unlikely the tipover switch is stuck, but, it never hurts to eliminate issues.
As for the alarm, it tends to be When they fail...not if.
I would remove it all, and bet the probelm goes away, or that you at least find that it was the alarm that caused another problem.