As I already said, I had this years ago, maybe it was with the Audi adapter, maybe it was with the Nokia 616. It appeared out of nothing and it disappeared again without any change. I did not fully investigate what exactly happened, maybe I didn't have HCI logs back then. Since the adapter aborts the pairing process it is most probably a problem of your adapter. Also since it happens with two phones with your adapter and didn't happen with my adapter and my Nexus 6. Maybe it will go away like it did for me back then. It looks a lot like a software issue.
Try to remove all pairing information from adapter and phone, then try again. Pull out the adapter for a few days to let a possible battery run empty. Maybe that fixed it for me because I only powered on the adapter once in a while. Try to pair a phone with handsfree. Maybe that fixes the adapter's internal state.
The only thing I'm sure of is that I cannot fix the problem in my app.