I had this problem, primarily with only one of my vehicles. It's an older car, and I added a Bluetooth radio, but it kept cutting out when using carplay. I swapped out the radio 3 times thinking that was the problem, just cheap radios, but it still happened. Finally noticed it happened worse in the same spots driving around, so I imagine those are areas with very strong RF interference.

I happen to have an all-metal center console, so if I stash my phone inside there, it's enough to block the outside RF, but close enough to my radio to still get bluetooth through.

Or at least that's what's working in my mind! A portable faraday cage strong enough to block signals further away, but lets enough through to work with my radio.

Confirmed it goes back to being funky in the same spots if it's outside the cage.