My imported skinned mesh's vertices act funny

I made a character in 3ds max and skinned it with regular bones. When I imported it into unity, some of the mesh's vertices will not morph like they do in max. It causes the character to pinch in areas like the arm and look shoddy overall. I want to sell this character in the assest store, but can't figure out how to fix the skin. Why doesn't unity exactly mimic the way I skinned the mesh in max? The character is otherwise perfect when animated in max, and I don't get any errors when I export it. I've tried remodelling the character, reskinning the character, but unity keeps animating it incorrectly. Any help is appreciated.