Android auto needs to connect to the car's head unit via USB and shares data through the cable. For the past few builds, the head unit hasn't been able to communicate/share data with the phone. Common issue is bad cable, but the issue is persistent for me.
I think you already have it being installed as part of the img file as a system app. I'd actually prefer to try it as a standalone/user app to see if that helps.
Android auto is known to be buggy for connecting. But it worked well back in March-April or so, then disappeared in the past 2 or 3 builds.