@480_s , can you confirm if you’ve triangulated your mesh before importing into Studio just like @WhyIsThereALengthLim suggested? Faces with a lot of vertices can be difficult for Studio to triangulate on its end, and will result in errors similar to what you have there.
I go into more info in this post: Cup Mesh Importing With Holes - #11 by Aotrou
DO NOT SUGGEST THE SOLIDIFY MODIFIER.
It’s bad and breaks meshes. Do not suggest it as a “fix” for inverted faces (because it doesn’t). Do not use it to “fix” inverted faces (because it won’t). And shame anyone else suggesting to use it too. This is a thing I see way too often.