Game Won't Save (Tips)Try these troubleshooting tips below to see if they help.
1. Move the Mods folder to the desktop for testing purposes. As they may have been broken or become outdated with each new game patch. See post linked below for more information. -- This will not delete the files.
Custom Content and Mods (Install/Remove/Organize/Fix)
http://www.carls-sims-4-guide.com/forum/index.php?topic=23495.msg410220#msg4102202. Something in the save system may be causing some issues. Go to the saves folder (Documents/Electronic Arts/Sims 4) and restore or remove the slot_00000001.save file if you have it. This is the autosave file. It is no longer in use by the game and can cause issues with the game loading or saving.
How-To: Restore a Saved Game
http://www.carls-sims-4-guide.com/forum/index.php?topic=21519.msg387147#msg3871473. If you have more than 25 saved games, move most of them out into a folder on the desktop and try loading and saving the game again. -- This will not delete the files. It only moves them out of the Sims 4 folder for testing purposes.
4. Move old screenshots, and videos, to a folder outside of the Sims 4 folder. - These can be moved to the desktop or a USB flash drive for safe keeping.
Moving some of these files may help lag/freezing in the game. - Moving the screenshots and video folders will not mess up the game. The folders will be regenerated. This will help lessen the load on the game due to the large size of the screenshots and/or videos.
5. Delete Game Cache and localthumbcache.package file from \Documents\Electronic Arts\The Sims 4 Folder.
http://www.carls-sims-4-guide.com/forum/index.php?topic=29288.msg401662#msg401662-- May not help with saving issues, but is good for troubleshooting purposes. It also helps "fix" some gameplay bugs.
6. When saving games, use Save or Save As using a similar name. This will allow for a save to go back to if needed. Game progress is less likely to be lost. Using Save and Exit can cause issues.
7. Check the Sims personal and family inventory. If they have a lot of stuff in either inventories. The game may have issues with full inventories.
8. Try Resetting your Sims 4 folder Aka Sims 4 Factory Reset - (What & Howto)
http://www.carls-sims-4-guide.com/forum/index.php?topic=29292.msg401669#msg4016699. Repair Game may help. - Right-click on the Sims 4 icon in Origin and select Repair.
Note: This post has been locked as it's for informational purposes.
