this is a known issue caused by an certain adult mod that can't be named. Are you using that one ? I have found it to affect saves even after you remove the mod but haven't found a solution to fix it.
Maybe just putting back the updated version of the mods helps ? Could you try that ?
@PLAYERBRITNEY There's not only one cause of this. You can test "vanilla" to confirm that removing mods brings Sims back: Drag the Mods folder to the desktop, delete the file called localthumbcache, open the game to test, and exit without saving.
To figure out which mod is currently causing this problem, you can do a 50-50 . I don't know of a recently broken mod that causes this, but you can check the lists in Broken/Updated Mods & CC , especially "Previously Broken"
