My sim is a male. Guitar, cooking, and writing hobbies have been maxed. So yoga was the next option.
First day of the hobby, everything was okay. Second day, when the sim did yoga and changed into yoga attire, the body changed into a female--just the body, not the face; so, imagine a male head on a female body.
During the yoga session, the attire would change after sim took showers; the male remained but the female body was still there. After the session, the body was changed back to male.
I changed the outfit to gain tokens. I discovered that the gender icon was changed from male to female even though the sim is clearly male. I switched the icon back to male and my original sim was deleted and there was a male model sim with a different name instead. So, I created a new one. And went back to cooking hobby to prevent the gender change.