yah, originally the udims were exported out of substance painter
with changing the names to the BaseName.####.[Support Image Format] suggested in the docs
all files were png, some files were 8bit some were 16bit
a few of the 8bit ones I re-exported out of photoshop with png with the highest comression since that seemed to work well for the 16k textures
in the end UE still imports the udims in the wrong slots,
so for me, merging the udims seems to be the safest route
but is quite a few more steps in the pipeline I’d rather avoid if I can get the udims working