It's a sys7 and the driver board is supposed to have wire links in switch matrix col drive lines. I believe this was to handle more simultaneous activation of switches. If you have a driver from an older game maybe it still has the resistors in place. Could be worth removing them?

I don't have a game manual but is there a chance it can be a setting to change the drop reset behaviour? Unlikely I guess, particularly as you describe your tests, but worth a look.