Could Be a bad switch compacitor. For the switch right here before the saucer in the chamber.
If one ball drains does it end the ball?(bonus count). Does the moto value increase when this happens?

Boiled down it's one of two issues.
The switch above the saucer is gettin miss read.
The selonoid is getting fired when it shouldn't be.

Pick a route and start diag. Do you have another Bally/stern with a compatible selonoid driver board? Or test that transistor. Or replace that transistor and the cap on the board. Those caps can go bad and cause goofy stuff to happen.

Disconnect onenor both wires to that switch. retest. That cap can also cause troubles. They are cheap and could just be replaced.