Phone updated yesterday (N920VVRU3CQB9) and besides the new interface a annoying issue has started. I may wear a headphone or ear bud connected to bluetooth. When I get in the car the phone will auto switch tot he BT car system or if another previously paired device initializes the phone will switch. I cant find any settings for this. I have turned off Battery optimize as one forum suggested, I have stopped all BT system apps, I have rebooted several times. Sometimes it drops the connection to the headphone/ear bud and doesn't connect and goes tot he phones speaker only.If I disconnect a devices in the BT Paired Devices list it does not auto reconnect. There has to be something else managing the BT connections that is misconfigured.
disconnect, have you tried re-pairing since the update??