Tarnished pins/cold solder joints J101 (far right on driver board)
Tarnished pins/cold solder joints J102 (far right on driver board)
Tarnished pins/cold solder joints J114 (far left on driver board)
Tarnished pins/cold solder joints J210 (right side on MPU board)
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This I find most often with resets.
So if you reseat these connectors and it goes away, likely need to replace some or all the female wired connectors and resolder or possibly replace the male connector pins if tarnished.