Okay, I'm going to resurrect this thread, as I have the same issue with my Fireball as the OP, but didn't see a solution posted.

To re-cap: At the start of a game, only one ball is put into the shooter lane. Everything works as it should during game play. If you lock a ball in the Odin or Wotan scoop, two balls are released into the shooter lane--one at a time--the ball release solenoid fires two separate time.

For trouble shooting, here's what I've got so far:
-This happens with Odin or Wotan Hole. They both exhibit the same behavior.
-With no balls in the trough (and a ball locked in Odin or Wotan), I can manually close #1 trough switch, and the ball release solenoid will fire continuously.
-The ball trough switches are gapped rather far, but still have a nice wiping motion when activated.
-The trough is clean, and the balls roll down freely, with no hesitation.
-There is not a hold relay for multi-ball as shown in 4MBC.
-I have visually checked the Odin & Wotan relay, and all switched appear to be in proper working order (although I did not use a meter to confirm)

So, what should the next steps be?

Thanks

Sure, I'll give that a try tonight.

However, since it doesn't happen at the start of a game (when all 3 balls are in the trough), I can't see how a non working trough switch would only show during a ball lock. But then again, I still struggle with schematics so I could be missing something simple.

We have a winner!!!

I started checking continuity on the trough switches. Everything was okay, until the trough got bumped or a switch activated.
631EB5CA-E798-4A32-8A60-9B4A220BBB8A (resized).jpeg

I removed all the switches from the trough and everything checked out properly. Upon further examination, I found that the fish paper was shifted, causing the wire switch to make contact with the leaf of the switch, shorting it to the other switches.
E2DB545B-AD94-47E3-A956-9A7A3101A9A5 (resized).jpeg

I tried loosening switch stack and moving the fish paper, but it didn’t seem to be wide enough. So my solution was to add some heat shrink to the wire switch.
C57EDE79-D1F8-4433-92B5-949E45F2454D (resized).jpeg

And problem solved. Odin and Wotan are now behaving properly.

Thanks all for the insight everybody!!