Quoted from Elfman:This is indicative of maybe a couple things. The front lip of your ramp could be damaged (or chipped off entirely, mine was when I got it) or the metal ramp in the garage has come out of alignment. Not impossible but that metal ramp is pretty sturdy so I am thinking the former issue is at play. It only takes a little bit for the ball to lose momentum and not make it to VUK to the upper playfield.
So I recommend taking off the upper playfield and asses the state of the garage ramp.
Thanks for the feedback Elfman. Here's what it turned out to be. The switch arm in the garage was scraping against the left ball guide. So if the ball was going at juuuust the right speed, it would get caught by the sticky switch arm. This is why it only ever happened a couple of times. Imagine the odds of a ball having enough momentum to get over the gap, but not enough to push the switch out of the way, and get stuck on the back side of the ramp being held in place by the switch arm pressing against the ball guide. This is why it was so easy to clear and felt like it was stuck on not much at all..as soon as my finger nudged the ball, the switch would give and all would return to normal.
I bent the switch arm a little to clear that ball guide and all fixed 100%.
Man I love this machine. And the kids are NUTS for it. Best, kid, theme, ever.