Is the ball still in the mystery hole? If it is, try removing it manually and dropping it between the flippers. It’s possible that will fix everything other than what originally caused it to stay in the mystery hole (maybe a loose wire on the switch or coil).

I base that on the fact that on my Genesis if a ball is in the shooter lane when you try to start a game it exhibits the exact behavior you describe, until the ball is plunged and drains...different era of course so not sure if that’s it, but wanted to post that just in case.