OK, so had a weird bug last night. On v20, infected off.
We were playing a 2 player game. A ball got stuck on top of the robot pop bumper and didn't come off with ball search (maybe make the robot move more during ball search?). So the game kicked another ball out which was cool at first since we could play and finished our games.
Then we started another 2 player game, game said a ball was missing, but the game started. However, once the ball that was stuck came unstuck, things got weird. When one of the balls drained, the game showed the ball over bonuses, etc., player cycled, and another ball kicked out. I can almost expect this. Then the 'extra' ball that was floating around the playfield drained. No ball over animation that I remember from that one.
Now from this point forward (above happened on ball one) the game would randomly end the ball in the middle of playing the ball. It did this for all remaining balls of the 2 player game.
A reboot seemed to fix it, but if it sounds like a hardware issue, let me know what to look for and I can check that tonight/tomorrow. It really felt like maybe a memory stomp or the total ball count in the trough got off and stayed off. It probably would have been better to not allow a game to start if a ball was missing, but it was really nice to start the games without taking glass off to fix the ball since balls can get stuck on RZ where you can't even see them but they usually come out when you play.