FIX THIS PLEASE

ktppddmx5b8g  Please try a new save and let me know whether it runs properly.  If it does, save your main household to your in-game Library, quit, load the new save, and place your sims there.  Let me know how it does.  I'm not saying you have to abandon the new save, only that this is a useful test.

If the new save has the same issues, drag the entire Sims 4 folder out of Documents > Electronic Arts and onto your desktop, and when you launch the game, a clean folder will spawn with no content.  (Your saves and other content will be in the folder you've moved but temporarily not read by the game.)  Don't add anything to the new folder yet, not even a Gallery lot or sim; just start another new save and let me know how it runs.

When you've loaded a new save, have a look at CAS and/or Build/Buy to see whether the kits' items are showing up.  You can filter by kit, and if the new ones aren't installed, the game will tell you you don't own the content.  It doesn't mean you actually don't own it; this is just the default message for any pack or kit that isn't currently loaded into the game.