Hi Steve
To "really talk" about Your pin and its problem: Please show us the snippet of schematics as I show from two other Gottlieb pins (take a picture of Your paper-schematics with the camera on Your mobile phone --- they usually make JPG-pictures).
"Buckaroo" has a relay for every Pop-Bumper --- "Hearts and Spades" has "ONE Relay actuates TWO bumpers" --- and Your pin ?

Non-pleasing is the "intermittent / sometimes".

Maybe "residual magnetism" on one or more relay(s) - want to try "sneak-in a thin paper between the armature of the relay and the coil of the relay" --- (((pulling strength of magnetic force weakens with distance, rapidly))).

See in the JPG - inital current flows to the coil of the relay along "my green lines" - the relay pulls-in, actuates all switches - so closes its Self-Hold-Switch*** - along my "red lines" is Self-Hold-Circuitry established.
Self-Hold-Switch*** - see on the "J-Relay": A short wire runs from one side of the COIL to an SWITCH mounted on the relay --- THIS is the Self-Hold-Switch***. Want to try "sneak-in a stripe of paper into the Self-Hold-Switch(es)*** to keep them always open --- then play many games. The playing is not as good as without sneaked-in stripe of paper --- BUT it gives us the answer to the question: fault in "my green wiring" or fault in my "red wiring". IF (if, if) the fault still happens: The cause is either residual magnetism or "in my green wiring". Greetings Rolf

0Hearts-And-Spades-Work-05 (resized).jpg