I believe I have tracked down the culprit of the drop target (left of center) that wasn't cooperating. I've attached a very close up image of the drop target assembly. Notice how the black (circled) plastic piece is sort of cupped? It was catching the edge of the tab on the drop target harder than it should. Filing it down with an emery board was just enough that it let go at a comparable moment as the other 3 targets. I was able to identify this by using a long Q tip which allowed for a larger range of gradation in pressure than touching with my finger.
Testing with gameplay afterwards yeilding success again and again, until one shot didn't register but it was more of a glancing blow from the far right side (opposite of the spring) so I hope that was a rare occurrence. More testing will commence.
I hope that this information is helpful to others that have the same issue.
Culprit (resized).jpgIMG_1475 (resized).JPG