All bingos have a feature called 'guaranteed advancing odds' which was a feature coined during the one ball boom of the 1940s. Early one balls would randomly place your odds anywhere on the board and each coin put your odds in danger of major change.
Bingo odds should never go down. You have a fault somewhere that is causing your odds to go up and down - probably just a minor switch adjustment needed. To help you narrow that down, I'll need to know more info: 1) Which odds are increasing? 2) During which button play do they increase? 3) Is there any rhyme or reason to it (like, only on replay play?)
If the first ball doesn't come up on its own, I'd suspect dirt or a slightly maladjusted switch in your trough. Specifically, the farthest switch to the left (the 8th ball). This switch is directly tied to the lifter on game start. Your shutter switches also play a role here, so if that trough switch looks ok and reasonably clean, I'd look at the shutter.
If it is scoring appropriately otherwise, these are relatively minor faults. For the step-up/down, I'd suspect that you have some broken down wire insulation somewhere. Since the bingos only step up/reset (remember, odds never decrease) you might also have some gummy odds steppers that are causing the whole problem...
Have you hand-tested those odds steppers, by any chance? If not, turn the game off, go to the back, and locate the odds steppers (around the middle of the back door). Push in the plungers one at a time until they hit max (8 steps), then reset. Then do the same to seven steps. Each time, ensuring that the stepper steps crisply and smoothly to the next step and resets all the way quickly to pos 0. Carry on doing this all the way down to pos. 1. And do it for each color (red/yellow/green).
A fault in the mechanical action or electrical contacts due to mechanical funkiness could possibly cause this, I think.
Regardless, I always check for stepper action on any new (to me) game - just to make sure it is stepping reliably and the steppers are reasonably clean and gunk-free.