One thing I can think of looking at these videos and the code, is maybe your enterHead switch is registering twice when a ball enters the head. Could you check this in switch test and adjust the switch? I understand this could be fixed in code but that's not an option currently.

Thanks, Koen

You mentioned on the DP forum that your start button double registers as well. Maybe this causes issues in the game launcher as well, by launching a double PinMAME instance? This is purely theoretical, because the code actually is designed to prevent that.
Anyway, to rule this out, connect a keyboard to the computer, and navigate the game launcher (Williams <> DP selection) with the keyboard:
N = left
M = right
1 = start button
Select Williams software and the correct face with the '1' button on your keyboard and see what happens.

Come to think of it, you mentioned that the 1.0 screen did look better in an earlier version (but too big), if that was consistently the case then it's probably not your start button. If the above doesn't help, can you share a picture of the earlier version's 1.0 screen? Just want to confirm it looks the way I expect it to.

Thanks, Koen