I've had very similar intermittent problems, as described in the thread below.
https://pinside.com/pinball/forum/topic/cftbl-mystery-light-outage
I've got no technical skills whatsoever, so I ended up jiggling my bundles of wires under the playfield and it started working again. My hunch is that it was a short of some kind. Who knows whether that's the source of your problem.