Wrong colors in JPG after Export for screens from CMYK color space
I had an issue when Exporting from a CMYK document with the Export for Screens... Option. I exported an artboard with a white (0, 0, 0, 0) logo on a black (0, 0, 0, 100) background and it turned out as a completely black JPG. I tried to change Export settings and colors but it always turned out wrong. As soon as I changed the color space to RGB it worked correctly.e
I have similar issue here. Sometimes I am exporting assets for printing like word templates, footer headers etc. Ai export PDF files into RGB which completely change the color space.
Check Overprint Fill option for your white art.