When the target drops, there’s a “finger” going through it that pushes on the switch that handles scoring. There is a lot of friction with this swiping action. If the backside of this switch is gummed up with old grease, the finger will drag too much and stop, leaving the target partially down and the scoring switch closed.

Unscrew the switch stack, clean the old lube off the switch, polish it with a wire brush attachment on a Dremel, add a drop of Super Lube on the blade, screw the stack down securely, and adjust the blade for good make-break action against the finger that actuates it.