I have the 2XL with a SONY Android Auto Aftermarket Receiver in my car. No issues with phone rebooting during a call. I do have some other issues though, like sometimes the audio will still be going through my phones speakers instead of the car, sometimes theres no audio at all. Both issues require me to unplug the phone and plug it back in, and 100% of the time that resolves it.
These issues were also prevalent on the OG Pixel though, so i cant say this is specific to the 2XL. Sorry for those having reboot issues, that would be annoying. BUT Android Auto seems to still have a bit of buggyness to it. It seems lore likely it is the cars receiver than it is the phone.