Quoted from schudel5:

It's a switch issue. The switch or switch actuator needs to be adjusted to allow the ball to fully press on the actuator and keep it pressed down. If the ball doesn't fully depress the actuator, for a minimum amount of time, it won't register the ball is in there. I had the same issue with Metallica for both the snake and mystery scoop. My DP has been fine and registers 100%.
I know it seems counter-intuitive that it kicks the ball out but won't register the shot. I believe Stern has code where if the switch is pressed and unpressed in a small fraction of time it fires the VUK and doesn't register it for modes or scoring. The ball has to settle in there and keep the actuator pressed for a certain length of time for it to tell the CPU the ball is actually in there. Sometimes loosening the switch, rotating a little and re-tightening or simply slightly bending the actuator is all it takes to get it to work correctly.