What the title says, after loading i got the message for migrated content and all Car and Warden entities were gone
I'm assuming this is unintended since i can't even pick up those vehicles and place then again like the description says

I think I'm experiencing this too. After some update, the AAI Car and Warden both come up with broken entity names and some busted functionality.

Since this thread might still be useful to the author i should add that i was using only the AI versions of those vehicles, and the car had a top speed of 45 km/h making it very unusable.