That problem appears to be a bug, as confirmed by this post:

I don't know the poster, but a Chaz does support at Stern and Chaz isn't a common name. I like the chances of your problem being fixed with the next update.

This is a mechanical issue. Saw it on a new location pro yesterday. All three targets were rejecting shots from the right flipper. On the other hand, the pro at PAGG rarely had the problem. It may be a break in issue. The game at PAGG was hammered nonstop all weekend.

The op was working on the one that was sticking yesterday. He pointed out that it's nothing like the drop target assembly on WOF. Virtually everything looks to be new except the targets themselves. If it was my game, I might try some dry lube. Otherwise, they may (hopefully) just need break in time.

I've seen this too. This is actually a third different issue. The front drop target is getting phantom hits. You can tell because the display shows you being awarded 2X bonus, but the target stays up (because it wasn't hit).

The targets use some kind of new opto/sensor. The edge of one side of the targets are painted black on top. The opto/sensor detects the changing light. No receiver. Hopefully those sensors aren't buggy. The assembly does look much more streamlined than the WOF assembly.

If my game was getting phantom hits, I would check the target edges and sensors closely. Make sure the part that's black is all black. Use compressed air on the sensors to blow out any dirt or dust.