Loading UDIM masks from SP "Warning: Mismatched UDIM image formats"

I am trying to load black and white mask maps as UDIM from Substance Painter.
Basecolor, Normal and all other maps load fine, but completely unable to get the masks loaded as UDIM. I am getting “Warning: Mismatched UDIM image formats”.

The naming is this- (these work)

And for the masks this (doesnt work at all)

Would someone point me in the right direction?