These kind of oddball experiences can drive you nuts. I'd check the wire loom to see if it is rubbing an edge somewhere. More than once I have had some loss of wiring insulation where the loom may ride against a metal edge or back of the playfield. You raise the playfield and the wires move just enough to eliminate the problem. Setting it back down and wear among a couple wires lines up and causes a short. Of course it could be something else entirely but I like to look for these type of anomalies when things get weird.