Quoted from Rensh:That’s a puzzling one. When you shoot while lock is lit, do you see the diverter trying to move even if it’s just a little?
Other idea, you test with a finger or move ball manual I assume? I have had cases were that worked perfectly but not while flipping. It turned out that the playfield windows wasn’t flush with the playfield causing the ball to ‘jump’ and thus missing the opto. Does this description fit with your issue ?
I had a similar thing. We figured out that it was sun light coming from the window (righthandside) when the sun was low. It interfered with the opto. So maybe this could happen.