Not quite sure if that's caused by the same issue I had, but if the blotchiness is from the toner flaking off after printing, increasing the fuser heat setting (Menu/Admin/Maintenance/Adjust Fuser/Plain) should fix it, as had that issue (similar-looking result to the photo) just with magenta printing 100% colour.
Otherwise would try adjusting BTR setting (same Maintenance menu) or doing a BTR refresh, looks like an issue that setting might fix as well, but beyond that I don't know what else it could be