The Bluetooth connectivity problem is Apples' problem not car manufacture's problem or some other device? Rebooting and clearing out data are bandaid fixes that are temporary and not a cure. Can someone (insider) say when this might be fixed?
I personally don't have any BT issues with my 6 Plus but that doesn't mean there isn't a widespread problem. Contact Apple and see if the issue has been reported and what they suggest you do or make a genius appointment.