I’ve been refurbishing this game for a while now, so I’m pretty familiar with it. I had different things to troubleshoot than what you’re battling, but I think I can help. I would look for stuck switches on the 3 strike bonus unit. The first thing I’d suspect is the switch on the 1 to 10 relay that is fed by the impulse cam on the score motor. I’m attaching a picture of that area of the schematic with the path highlighted.
It would be better if I were in the same location as my game right now, but I’ll do my best and I’m sure others will chime in if they see something that I missed.
Good luck,
Dave