Pin 3 is D0 from the MPU.
Pin 11 (not pin 10) is the clocking signal from the ASIC.
Why the behavior changes when you measure between those I can not say other than the logic level of the pins is being changed.

I would say that you have a big coincidence here.
For whatever reason, the driver board picked this moment to fail. Most of the time, the issue is the the LS374, but removing that IC cleanly is not trivial.

As always, "divide and conquer" is a good strategy.
Swap this driver board with the driver board in one of your other games.
See if the problem follows.

BTW--This is NOT a ground problem.
--
Chris Hibler - CARGPB #31
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