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Try "Reset Network Settings" on the iPhone and/or un-pair & re-pair it with the Beamer (i.e. forget the BMW's Bluetooth entry on the iPhone's settings, and remove the iPhone from the BMW side).
 
Fwiw after 9.2.1 I had issues also with my cars Bluetooth. First update ever that caused an issue. I am going to try unpair repair and hope that helps.
 
i updated my iPhone 6s Plus to the new software and all of a sudden the Bluetooth in my bmw 328i. Stopped working. Any ideas?
As versions come and go each changes how well bluetooth works with my car. At the moment, on 9.3 beta, things work well. On 9.2.1 I had trouble not with connecting but with keeping the call connected to the car. It would move from the car to the phone and back again several times during a 15 minute call. 9.2 just before it was pretty good at keeping the connection.

Point is, something changes in these updates that at times breaks this feature. With 9.2, it was broken for me on beta 4 then with the final release it was a carrier update only. Strangely, bluetooth was solid after the carrier update. I almost think the issues are more related to the carrier update portion than the OS itself when an update breaks bluetooth but just a theory.
 
I have some issues connecting to the Mobile Network after 9.2.1 update, it comes and goes.
Fixed after a reboot, at least temporarily.
 
my 6S plus Bluetooth continued to work just fine for all my paired connections, including my 2013 Audi S4... no issues here so I'm not sure how widespread this is.
 
I also had issues with intermittent bluetooth connectivity after updating, but another restart seems to have fixed the problem. It never made it to my car before the restart, but it was having issues with my watch and a bluetooth speaker.
 
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