My Theatre of Magic seems a little fussy, but I can't pin down the problem.
It ejects balls 1 and 2 fine. 3 and 4 it doesn't want to eject. Sometimes if you hit both flippers it ejects them. I have the same issue when playing, when testing the trough eject or doing eject balls in test.
Trough optos work fine. There was a plastic guide in the trough that was really dirty, I removed that, no effect. The trough itself doesn't seem damaged. So it feels mechanical in nature but I'm not seeing an obvious cause.