Levi here is a video of the action. I took this after a restore for a client. Maybe it can help. Watch the ball break the optos.

Also make sure your optos are working, Cleaned and aligned. This is the same for the drop target switch which gets battered and misaligned often.

The switch actuator also gets bent a lot causing issues.

Did you test the wall down target switch # 51 in switch test?

Is its actuator straight and not bent?

Is the micro switch angle on its mounting plate correct?

Is the switch intermittent? Bad internals? Wires etc?

The lock switches must be adjusted sensitive to register without trapping the ball which they do very easily in that tight space.

Once again make sure the actuators aren't deformed and or loose with sloppy side to side play. Did their anchor pins get worn on the switch bodies? etc.

On all of the Shadows that I have repaired and or restored the issue you are having was due to the Wall down Microswitch being at fault for various reasons or the ball lock switches not being adjusted correctly.