Please try these steps. Specially let the game create a new sims 4 folder.
But before you do this. Save your Sim with this problem in your gallery. Now let the game createt a new folder. Go to your backup folder (if you don’t save your sim online) and copy your tray folder in the new folder. Create a new game and import your Sims from the gallery. Your Sim works now? Greate!
Now drag your sims4 save from the backup folder back and show if the sim still works. If it does your sim are saved when not, you have a corrupt sim (yes, this is possible; special with mods but is exceedingly rare)