Opened game to find half of my data gone

Sounds like your One Drive is backing up your pc. This happened to me too unknowingly. You can find Puzzleaddict's steps on how to fix that as well as my own by following this link. Try and follow hers first as that is the recommended method. You'll have to copy and paste because for some reason it is not allowing me to set it as a link. 

https://forums.ea.com/discussions/the-sims-4-technical-issues-pc-en/current-issue-sims-4-savesuser-content-disappearing-pc/11838402/replies/12257129

carsone2000​  Where is the game currently installed?  You can see the location in the EA App, under Sims 4 > Manage > View properties.  If it's installed anywhere in Documents, or another folder OneDrive is syncing, that needs to be addressed.

Nightgypsy​  Sometimes links don't work until you add a space after them and then press Enter/Return.  Sometimes it takes more than one try.  The URL you posted did turn into a link for me when I c/p and added a space afterwards, after a couple of seconds.

That is good to know and thank you, that was driving me crazy and I didn't have time to figure it out right then. 

puzzlezaddict​ When I click manage on the EA app under Sims 4, it only allows me to manage my add ons. However, in my file explorer on the hard drive, the EA folder is located in Documents. 

What's weird is that I haven't used my OneDrive in years because it ran out of storage and I never bothered with it again. This is all I use this computer for. I don't know why it was trying to sync 2 days ago. I am slightly concerned this means I won't be able to recover any game play from within the last 2 years that my OneDrive wasn't syncing. 

When I opened the game on the EA app it seemed like it was glitching out and then finally pulled up. Where I then noticed the problem with my HH's. While the loading screen was glitching I got notifications popping up related to my OneDrive. 

I have started the solution that Nightgypsy​ provided me, but since half of the EA Folder on my hard drive had red 'X's instead of green 'Checks' like the solution said, I have been offloading anything not Sims 4 related from my OneDrive and trying to get the OneDrive to sync it. 

Cleaning out your one drive to make space is important, but also remember that it is going to try and resync any folders that it was set to backup. In my case it was Desktop, Documents and Pictures.  So if you have a lot of pictures, documents and stuff on your desktop, you can save yourself some time by backing that stuff up to a folder or external drive that One Drive would not be synching. Disable your internet connection while you're working so you're not fighting One Drive as you go. Then you can copy stuff safely and delete it from the folders One Drive is syncing. Just don't mess with anything in your document folder that a program put there. If you're like me and have a ton of stuff like documents, pdfs and the sort that you save to the document folder individually, that is the kind of stuff I mean for you to put somewhere else and delete from the document folder. Then One Drive should have plenty of room to sync what is left and it won't take as much time because there won't be as much for it to upload. I hope this makes sense and helps.

carsone2000​  There will definitely be an Electronic Arts folder in Documents, but that's not what I meant.  I'm talking about the game's program files, the Sims 4 folder with subfolders like Data, Delta, Game, etc., as well as one folder per pack you have installed.  That's what I wanted to know about—if that data is in Documents, it needs to be addressed.

The default location for an EA App install of Sims 4 is this:

C:\Program Files\EA Games

If you've installed the game through Steam, this would be the default location:

C:\Program Files (x86)\Steam\steamapps\common\The Sims 4

Point is, find this folder and let me know where it is.

OneDrive can reenable itself in a Windows update, often without it being clear that that's what the user is agreeing to.  The most reliable way to prevent this is to unlink your PC from your Microsoft account, since no MS account means nowhere for OneDrive to sync any data.  But you'd want to move your critical data out of OneDrive's folder before changing any settings, as covered in the first post of the guide Nightgypsy linked earlier.