Samsung S6 not connecting to Android Auto - VW App-Connect

[AC Question]

I have a Samsung S6, and have recently purchased a VW Sportwagon with it's app connect device, android auto capable. Initially AA worked and the devices paired in every respect. Then the connection gradually became erratic and now they won't connect at all. The car sees the phone, but continuously tells me the phone needs to be unlocked. I've taken all form of security off of the phone with no improvement, I've set security with a PIN, and seelected the car as a trusted device, still nothing. I'm not sure which device to blame, the car or the phone. Has anyone got a solution.