I came across a minor conflict with Late Night and various custom content 3rd party hairs.

It seems that some of the hairs restrict the muscle slider that came with LN.

I just stumbled upon this while making a Sim and I couldn't figure out why I couldn't use the slider. I started eliminating various things, changing the skins and finally decided to see if by small chance it could be the hair. And it was.

I don't have a list or anything for you, so you will just have to trial and error it.

Hope this helps someone.

Edit: You may already know this but I'm going to post for those that might not. I'm also seeing the hair changing when showering or bating and some hair they bathe with their shoes on. Same old things when just the base game was released and we started adding cc to our games.

Hope they fix it.