When I owned Nip It, I also had he same issue. I found that the metal part the kicks the ball into the trough was worn and would sometimes kick the ball into the air which would slow the travel time to the trough switches. From memory, I bent that part so that the kick of he balll to the trough was smoother with no air balls. Also, I recall bending the metal above he trough track to prevent air balls. It was a bit ugly, but hidden under the apron. The ball(s) must make it to the trough switches quickly, or the ball count will not advance.

Have you tested the theory that there is a mechanical issue with the ball kicker? You could do this by removing he apron and manually activating he trough switches. You may notice some difference between when it works and when it doesn't. This ball trough process must be in perfect working order for the ball count to advance.

Maybe try to fix the ball kicker issue first to get the balls to properly advance. BTW, here is another thread that has some good info on nip it...in case you have not seen it.

https://pinside.com/pinball/forum/topic/bally-nip-it-forgets-to-advance-the-ball-count

The bonus unit on Nip It does not step down one position at a time. In addition to collecting the bonus when a ball drains, you can also collect the bonus by locking one ball and releasing the ball by hitting the release targets. The built up bonus can be collected multiple times in a single ball by locking and releasing the 2nd ball. The bonus unit only resets when the ball count changes.

Rolf,

Yes, the bonus stepper is a total reset unit. This is unlike most bonus steppers which are single step resets.