Check the reset relay, (on the bank in the bottom of the cabinet). Some switches may be making when they shouldn't because the overhead bar, (down the length of the bank of relays), attached to the reset coil, is binding up and isn't returning all the way to it's "Standby" position, (after resetting at the beginning of the game).
You can check this WITHOUT messing with the relay switches by first loosening the wingnuts, (on each side of the bank of relays), lifting the entire bank out of it's housing, and letting it rest on top of the housing. Don't worry, nothing will come apart, it's hinged. Play a few entire games with the bank in this position to see if there is improvement.