Take the balls out the game and see if they are magnetized. Easy test is to place a small screw near them. All you need is two balls magnetised to attract to each other in the trough and this problem will persist.
I had exactly this issue on a JN, and it only presented itself once TWO magnestised balls were next to each other in the trough.
It could be the trough itself, but it sounds like you ruled that out. It is not the Homepin board. I'd look at your balls
