I have had this problem when reloading scenes with multiple characters. It always seems to be the hip part of male figures that disappears for me (guess that's because I usually use standard males with Thorne's females). The method I've been using to correct this is to save the pose of each of the males, put them into the "default" pose which makes their hips reappear, and then return them to their pose for that scene. Problem corrected. Some of the suggestions above seem like a better solution though. I'll have to try them.