before you do anything else, take the apron off and check the physical operation of the switch. Does it "click" each time the ball comes to rest on it? If not, you just need to adjust the wireform so it pushes down further when a ball sits on it. Your switch edge test in the settings menu can also help you here by giving you visual confirmation on the screen.

It's probably not going to be that easy, but until you verify mechanical operation of the switch there isn't much point in poking around any further.

If this doesn't work, there are some specific tests you can do while you are experiencing the problems during gameplay. But let's eliminate the easy stuff first. Good luck.