Help needed on a WIP! (Marvelous Designer)

what were your export settings from MD? and was the uv like this before you retopologized it or did this happen after?

the link you posted didn't go to a photo of your export settings. and did you follow this tutorial when converting your mesh? i suggest exporting your md object as tris and then following the tutorial to retopoligze it. if you still have the same issue, try selecting unified uv coordinates when you export it from md

well if you can't retopologize it there is no reason to export it as a quad mesh because there is no easy way to decimate it without it converting back to a triangle mesh. just export it as tris and check unified uv coordinates.