There are two relays in the backbox of Chicago Coin machines that use a double row of leaf switches on them (typically right between the score reels on two and four player machines). Armatures on those relays always seem to be broken and cause all kinds of issues on CC machines. I would look at those before I wasted a lot of time on anything else. From my experience those relays have issues over 90% of the time on CC machines.

Score reel contacts can also be a PITA on Chicago Coin machines!

Now I feel like an idiot - I looked at post again and realized you are working on a Bally machine not a CC machine. Reset bank looks like a CC so I was thinking CC. Never mind about score reels but relay could still be your issue for sure.