If you are receiving double bonus and neither J nor LB are actuated, check out these two switches on the attached schematic. If either one is misadjusted and open, I'd think that would result in "double bonus-like" behavior. You'd get 2 bonus subtracts and 5000 points per motor cycle.
S76 double bonus error (resized).jpg
As MarkG and Garrett stated above - the torque applied to the relay bank, if it is not firmly seated and the wing nuts tightened securely, might be the cause of the switch on LB being out of adjustment.