I might be a little late to the party, but its 100% a switch issue. Both GBs I have access to had the same exact problem, pop the hood and you will find that the switch is loose or hanging on by a thread. The switch tests fine because when testing with the hand, you're just looking at whether or not switch works - it does.
When ball enters the equation, it will very often "bounce" in the scoop and because the switch is loose, it will trigger for a split second, but not stay depressed. Software is there to immediately kick it out instead of awarding you the points because the switch registered, but did not stay held. Same behavior is sometime seen with the right scoop when the ball doesn't quite get to sit in it, the ball saver will activate, and the solenoid will fire, but no award is given.
If it still happens on your location, do let the op know to readjust and tighten that switch.