Have a V10 and Pioneer AVH 4100NEX....Android Auto works fine. Connection good. Music from phone or apps (Pandora, TuneIn, etc) all work. Problems are when I try to play media when only connected through Bluetooth (i.e., when not connected to head unit through AA)....here connection Bluetooth drops completely if I launch any music app. I then have to turn Bluetooth on and off to re-establish Bluetooth connection, etc. I cannot get media to play at all unless running through AA. Kind of frustrated because I don't want to be limited this way.
I have a Bose Bluetooth speaker which works fine in this regard so I fear it's an issue with the phone and Pioneer head units. Tho I've seen posts in other forums reporting similar problems with non-Pioneer head units