I don’t own a car, because I think cars are one of the biggest threats for survival of mankind, so I can’t test with car system. But that is maybe slightly off-topic.
On Topic: I had to delete the BT connection in the Settings to my Bose Sound link Mini II (a BT speaker) and pair it with the phone again, otherwise I could make no connection between phone and speaker with the August 1st update of LOS4MicroG 17.1. So there seems to be an issue, but for me it could be solved by re-pairing.