I have the same problem where every say, 100th time the ball drains in the lower playfield, it rests on the track switch ahead of the return kicker, and it's like it has been sucked in to a region of spacetime where gravitational acceleration is so strong, not even visible light can escape.

I have checked and cleaned the leaf switch, but even if I open up the machine, reach under and actuate it manually, there is no response. It seems like a problem somewhere in the brains, and not mechanical. ‍