Android Auto won't launch on headunit

[Android Central Question]

I have a kenwood ddx9017dabs and Samsung s8+. Android auto used to work when headunit connected to phone via Bluetooth. Not any more. Android auto will only launch on headunit if usb is connected. Headunit will connect to phone via Bluetooth but Android auto won't launch. The airmirroring logo remains (it used to switch to Android auto) once the phone is connected. This is only recent. I think an update has put it out of whack. Any ideas how to get Android Auto to launch on headunit with Bluetooth connection?