Also had a Baywatch I fixed with similiar problem. The ball trough opto was hacked so threw this out and replaced with a new set from AMD. Also found a couple of diodes had come loose off some of the switches especially on a couple of the targets which I think are on the same row/column as the ball through. Also on DE/Sega games,  dry joints on the PPB board headers and relay can cause the game to kick an extra ball into the shooter lane.