I have discovered an issue with several models of newer VW not correctly reporting signal strength nor network when connected via Bluetooth.
After some discussion on element and conducting an experiment, it appears to be Google Play Services related.
The steps I undertook are as follows:
Created a separate Google user profile and installed Android Auto, which pulled in all the relevant Google Play dependencies.
Connected phone to car with existing, remembered Bluetooth connection. Car reported correct network and full 5G signal strength.
Disconnected Bluetooth and swapped to main profile with no Google Play services installed
Connected phone to car with existing, remembered Bluetooth connection. Phone connected with no issues, but car reported no network and no signal.
This no network and no signal state continues until a call is either made or received, which always come through with no issue, assuming I am in an area with signal.
This leads me to deduce that newer VW infotainment head-units are somehow expecting signal strength to be reported through Google services, and VW doesn't like the way AOSP reports signal strength. Probably needs to be fixed by VW, but I thought I'd report it anyway.
If this behaviour is unreproducible, I will attempt to make a video demonstrating the issues later when I have access to a second phone.