This definitely sounds game-related, as with challenges after awhile the game will get bogged down a lot and will become hard to play.
You haven't mentioned what you've tried to help relieve the freezing, so please forgive any repeat tips.
1. Move the mods folder to desktop (for testing purposes) - This is to fully make sure it's not outdated mods/cc or some hidden files in the Mods folder. - Read more in the post linked below:
How to Fix Problems with Mods/CC
http://www.carls-sims-4-guide.com/forum/index.php?topic=25031.msg426156#msg426156We recently received a new game patch (March. 20th) that has made some game mods and custom content become outdated. You need to go through your mods folder to see what needs to be updated.
Testing by disabling mods in the Options Menu, isn't enough of a test to be able to tell if it is a mods problem, a cc problem or a vanilla game problem.
2. Delete Game Cache Files (What and How-To)
http://www.carls-sims-4-guide.com/forum/index.php?topic=29288.msg401662#msg401662The localthumbcache.package can be found in the main Sims 4 folder
C:\Users\Username\Documents\Electronic Arts\The Sims 4
Also removing the mods folder without deleting the localthumbcahche.package file from your The Sims 4 folder, also isn't enough of a test. It all has to be done together!
3. Deactivate Origin In-Game - Open Origin, Go up to the Origin Menu, Click Origin and select Application Settings. Select the Origin In-Game tab. Make sure it is turned Off. - This deactivates Origin In-Game, as it has been known to cause problems with games.
4. Repair Game - In Origin, right-click on Sims 4 and select Repair. - Do note this repairs the game's install files for the actual game. It does not make any changes to the saved game files. Meaning that your saved games are safe, they won't be deleted.
5. Try a Sims 4 factory reset and a new game save without mods/cc.
Try a Sims 4 Factory Reset - (What & Howto)
http://www.carls-sims-4-guide.com/forum/index.php?topic=29292.msg401669#msg401669See post linked below for more tips:
Relieve Freezing and/or Game Lag
http://www.carls-sims-4-guide.com/forum/index.php?topic=29313.msg426179#msg426179