Okay, I don't know why it's making a lighter version, but I think I know a way to fix it.
Single-click on the mask thumbnail in the layers panel. Then press Cmd L to open a Levels window. Grab the middle slider and move it ALL the way to the left.
Stop wasting your time with that stupid function, period. Just mask it like a normal person. https://www.damiensymonds.net/2010/10/shift-while-brushing.html
Image Processor is really fussy. You have to have exactly the same versions of Photoshop and Bridge running. If you have the latest Bridge but not the latest Photoshop, or vice versa, it won't work.