Quoted from fnosm:
Probably getting stuck where the ball is returned after going through the OZ lanes. The area below the OZ lanes doesn't have mylar but where it rejoins the orbit there is mylar. This results is a 'ball trap' when a ball plunged lightly enough doesn't have enough momentum to overcome the mylar ridge. I have this happen all the time and it is an annoyance for sure. I reach up and shake the machine up near where the ball is stuck to clear it. If you can get to the side of your machine near the back box and look it is fairly easy to see the ball just sitting there waiting for your nudge to get it rolling again.
I have seen a fix for this (probably in this thread) where mylar was applied below the OZ lanes area, effectively eliminating the lip. It looks like it would be difficult to do a nice job of this without one of those craft cutters. BTW if someone is willing to do make some mylar that fits this area, count me as your first customer.
I thought it was the mylar edge, but mine is perfect.
Its true that a failed mylar would do this.
But in most cases it's a slipped rubber.
It's the rubber to the left of the mylar, and up a little to the left.
It's a little hidden, and hard to notice unless you know what you are looking at.
It slips up off its notch.
This makes a little corner that the ball can rest in.
Action from the sling does it.
I have had to slip it back down a couple times now.