About every third power up, my Elektra would have the same, one GI bulb out (lower left main playfield slingshot area). After numerous, adjustments, cleanings, wiggles, testing and bulb changes, nothing seemed to consistently fix this problem.

Finally, after removing the slingshot plastic and bulb in question to re gap and clean the socket contacts yet again, I barely noticed a small quarter inch sized sliver of thin, clear glass jammed into the light socket. It was practically invisible! Removed it and bingo, no more problem!

Since then I've kept a look out for evidence of smashed playfield glass or bulb shards in the cabinet bottom of any used or previously routed games. Two of my games showed evidence of this and on occasion small shards of glass have worked themselves free from wherever and suddenly showed up on the playfield! Yikes!