On my upper deck, i am pretty sure there was no magnet on the pitching unit. I do remember that on one pitch setting the bat resistance increased to make it weaker.
I will have to check what pictures i can find from when i had mine.

Not sure you can find it but there is a good photo of my pitching mech on my for sale ad from a year or so ago

I stand corrected. I looked at my post in the pitch and bat thread and there is a "curve " magnet.

Have you tried the game with the magnet NOT connected?
Has the pitching mech itself or the balls become magnetized?

If you look at my for sale ad the guides come to a point.

https://pinside.com/pinball/forum/topic/for-sale-williams-upper-deck-pitch-and-bat

There was a piece of plastic under the flap if irc . It held the ball in the groove before it launched.