Sims not being saved

Hi, I just downloaded Sims 4 last night and had this issue again. 

When I create a Sim and then another and go to enter the game, one of the Sims is never saved. The Sim always reverts back to its original look before I customized it - I thought this was a glitch but it's still happening. I can't save from the CAS menu, does anyone know how to stop this? It's really annoying since I spend a long time on my Sims.