Here's what I'd do first.
Look over the I/O driver board connectors. There is one directly above the voltage regulator (J16) that sends +5V to the CPU. That connector tends to get toasty and tarnished from the heat given off from the voltage regulator. If it looks brown, I'd replace it along with the header pins. I've replaced J16 on about 5 games that had reset issues and the reset issues all went away after doing that.
Next I'd reseat all the connectors around the edge of the board. Just in case one is flaky, but J16 tends to be the culprit.
Lastly test the +5V. Set your DMM on DC volts, black lead on ground braid, red lead on the bottom leg of resistor R114. If it reads below 4.9V I'd adjust the voltage up a bit with the potentiometer at R116. I've never had a low voltage issue with any Whitestar game yet. But check anyways and adjust if necessary.
I'll bet you have a bad J16.