I get this problem about once a month. Pull off the trough connectors and reseat them and it is good to go for another month. Seems like crappy connectors to me.

I also have the problem where the lower playfield ball drains and then does not re-launch. It just sits there and counts down and sometimes does a ball search if there is enough time left. Again, I reseat the connectors to the optos for the lower playfield and the problem is fixed for another month or so. I am seriously considering directly soldering the wires or maybe trying to find some better connectors. Anyone else have a permanent solution to this problem?

I don't know the specific reason for the connectors becoming intermittent, but my game is less than a year old and has never seen high humidity.