This isn't unique to the Symbioz and is more of a fault with Android Auto but it caught me out the other day.
If you use Android Auto and activate the OK Google Voice Assistance when in the Android Auto screen on the Multimedia display and then adjust the volume via the Multimedia stalk on the steering column when Google Assistant is speaking it locks out the radio volume control until you cycle the ignition.
i.e. if you try and adjust the volume after that all it does is adjust the volume of the assistant's voice and not the radio. This only seems to happen when using Google Assistance via Android Auto.
I was going mad trying to work out how to set it back to the radio volume and ended up turning the screen off so I could hear what the person was saying to me in the drive thro.
I had problems with Android Auto in my B8 Passat so didn't use it much then as a result, I think it will be getting binned again.