To fix mods and custom content try the 50/50 method:
1. Move all the mods and cc out into a temporary folder on the desktop.
2. Move a few files back at a time. Load the game to make sure it loads and everything is good.
3. Delete the localthumbcache.package from the Sims 4 folder.
4. Repeat steps 1 - 3 till there is no more files to check.
** While your testing, don't save the game. If you find any problems, delete the mod or custom content file.
How To Find Problem Mods and CC - http://simswiki.info/wiki.php?title=Game_Help:TS4_Finding_Problem_Custom_Content
Broken/Updated Mods: Python/Terrain Update + Get Famous, Nov. ’18
Custom content can become outdated with most new game patches. If the game works when the Mods folder is removed, then one or more of the mods and/or custom content has become outdated and will need to be removed or replaced. EA/Maxis aren't responsible for broken mods/cc. It's up to the creators to fix.
January - last edited January
Just wanted to say make sure that you did not accidentally add a sims3 mod, that will cause this problem.
Try resetting your user files as described in the factory reset described in this post: http://answers.ea.com/t5/The-Sims-4/FAQ-Troubleshooting-Steps-amp-Known-Issues/m-p/3621199
You won't loose anything. Just make sure to not delete any files and make a backup.
After renaming, repair your game by right clicking on the game in Origin.
Try on a new game with nothing added back first (start new game). If it works, put back your save game and try again. If it still works, you can start putting stuff back.
The rest does not need putting back, cause they are mostly cache files that recreate or log files that are not needed for the game.
I don't work or have any association with EA. I give advice to the best of my knowledge and cannot be held responsible for any damage done to your computer/game.
Please only contact me via PM when asked to do so.