Are you sure it is not a diode? I’m not sure how you could have tested all of the diodes on the playfield as you would have had to disconnect each one. TerryB has a great video on how to check for a shorted diode. If you can’t find it, I’ll post it later when I have more time. Also, check where those switches are in the switch matrix. I need to look at the manual which is not handy at the moment, but the problem may depend on whether they are all in a column or scattered across the matrix.

From everything I’ve read, you do.

I wouldn’t be surprised if it is a diode. Here is terryb video:

It might also be a short to ground somewhere, hiding on you.