Positive update from a last-minute effort last night.
1. Pop bumper switch confirmed not working. Coil works though.
2. It's no longer stuck on switch 9. Switch 9 is one of the coin switches. It was part of the wiring in the homemade coin-adder button. As soon as I un-soldered all the wires put in there, it finally went idle on the stuck switch mode. Before, it was always blinking 9, sometimes blinding it to other switches on the field.
3. Drop target sets smoothed out correctly. What's weird is one of the DT's switches(48?) pulses much slower than all the other switches. Every 1.5 seconds or so. Any other switch does it at a faster pace.
4. Correctly identified all the wires for all 3 coin switches. Only have a switch for 1, but can work with that. Would rather just flick the coin switch in the door than hit the button which was a bit overdone with wiring.
This just might get the game to behave a bit better.