Is the gameplay normal, goes through all balls, racks up bonus, etc?

You need to figure out what de/activates the relay, not what the relay does.

My last issue like this was because the 0 score switches were not all open.

Are your score reels resetting to zero?

It's possible that one of them may stuck at zero but the zero position switches aren't opening.

Using your finger, manually advance each score reel to the number one on all four players.
Then reset the machine and observe them as they reset. They should all advance smoothly to zero and stop, If any hang up or are sluggish, they will need cleaned and/or adjusted.

Not quite. The reset relay is first energized by the path that includes the switches for coin re AND game over re. The reset relay is then locked on via its own reset re switch and any of the 3 paths to its left on the schematic.

The reset relay will remain locked on until:
(bonus re switch) AND (all of 16 drum unit zero switches) AND (mb ind c switch - on the score motor) are open.

Capture (resized).PNG

Just like the score reels, the bonus stepper unit needs to reset to zero position such that it opens its zero position switch. This zero pos switch opening will cause the bonus relay to de-energize and therefore the bonus re switch in the top of the 3 paths above will open.

Is your bonus stepper unit fully resetting to zero such that it is opening its zero position switch?
Capture (resized).PNG

Jeff is on the right track above. Start with each of the 3 paths mentioned and figure out which one is not opening. Then work up that circuit to see where the problem is.

Mine was score reels where I had 1 switch that wasn't opening on 0. Took me a long time to track it down and I had inspected that one a couple of times. Using paper or business cards, you can start to eliminate which ones are working properly.

Your issue may be somewhere else, but you can use the same approach.