I haven't loaded my game up in a long time and today I updated my game, my mods, everything. When I opened up CAS I noticed my default skin was not on my sim. So I made sure it was there, yep it was. ...
You can also fix your default skin manually with s4pe, it's explained here: https://midnitetech.tumblr.com/post/631312122145587200/fix-default-replacement-skins