Origin Problem

Try clearing Origin's cache. If that doesn't work, uninstall and reinstall Origin "the hard way."

https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
https://help.ea.com/en-us/help/origin/origin/manually-uninstalling-origin/

This issue was supposed to be resolved a couple of weeks ago, with the recent Origin patch. Hopefully, the above steps will help. But if they don't, you can try one other trick (for Windows; there's a different trick for Mac OS).

• Sign into Origin, hover over your username, and go to Application Preferences > Application. Under Client Update, disable automatic game updates. Exit Origin.
  
• Sign in again, enable auto game updates, then go to your game library, right-click on the TS3 icon, and select Repair Game.
  
• When it's done, Exit Origin and launch it again. The download may start automatically. (This works sometimes.)
  

If none of this helps, please let me know which pack is affected. You can also post at AHQ, or I can get in touch with the community manager who was working on this issue the first time around.

Thanks. I'll give it a go.

@CharmedSlayer6 This does happen occasionally—the install process seems to hang right at the end. Sometimes it's actually fine, and after you restart your computer, you can play without issue; other times, you need to manually uninstall the pack and try again.

https://bluebellflora.com/manually-uninstalling-an-expansion-or-stuff-pack-in-the-sims-3-for-mac/

If Origin itself is stuck, you can run the reset tool for Macs:

https://help.ea.com/en-us/help/origin/origin/how-to-reset-origin-on-mac/