Changes in CAS not being saved

Do you have any mods or custom content (CC) in your game? Could you test without?
You can just move the folder to a location outside the Electronic Arts folder.
If the game works without your CC and mods in, your issue is probably caused by a broken mod or CC.
You can find a full list of broken/incompatible CC and mods since the Seasons expansion pack over here:
https://forums.thesims.com/en_US/discussion/941998/broken-updated-mods-seasons-june-2018-patch

If it still doesn't work I suggest taking out half of your mods and CC and testing the game. Then keep splitting until you find all that is broken.
Either update or remove the broken CC/mods.  

I do have CC, and have tried taking out my entire Mod/CC folder to see if I'm able to save any changes in CAS but still got the same result.

I haven't tried splitting my CC yet though, I'll try that when I get home and it'll hopefully do the trick. 

Thank you! 

Best thing would be to create a new The Sims 4 folder and test. 
- Go to Documents\Electronic Arts\
- Rename the 'The Sims 4' folder to something like 'The Sims 4 old' 
- Start the game, this will create a new folder.
- Test the game, if it works fine start moving folders from 'The Sims 4 old' over to the new folder.

I've tried taking out my CC/Mods again just to see if anything happened but meh, still the same with my CAS changes not being saved. 

I did what you told me and created a new Sims 4 folder, and the game was running smoothly and when I went back to CAS, it finally saved my changes. Now I just have to start moving folders from the old folder to the new folder. Hopefully, it's smooth sailing from here on out. 

Thank you!!

@dtang0224

It seems that your old savegame has become corrupted. This can happen on rare occasions when playing with outdated Mods/CC. Whenever there is an update to the game you should test if your Mods/CC needs updating as well.