Lags & Invisible, Frozen & Stuck Sims --> Post here if you have the issue.

You can't uninstall patches. You will need to remove your game completely and then just reinstall, manually patching to the level you want. Older manual patches can be found at Modthesims.

The cars only cause lags, they have probably nothing to do with the freezing and invisible sims. I'm still thinking that's unhandeled scriptErrors, namely the TestBarBrawl one. Cleaning up Cars is only a small aspect of overwatch. Try it before going through uninstalling.