Hi to all, I am struggling with BT on iPhone 6S as well. After iOS 10 update I am not able to use my Plantronics M55 earpiece/Car BT system for receiving calls anymore.
BT earpiece/Car BT system connects without problem, but when someone calls me and I want to pick up call on BT device, phone freezes, call is answered, BT device disconnects/connects and the call is hung up. It happens in 90% of all calls using BT handsfree device. If it happens only on this Plantronics M55 I would suggest it is the problem of this headset, but same thing happens also in my car BT system (Skoda).
What have I done? I went to an Apple service provider, they replaced my whole iPhone 6S for the new one (its in warranty), but problem persists even on new device! So I have tried to completely install new vesion of iOS 10.2. without recovering my iCloud backup, in other words I have set up my iPhone from scratch and problem is still in there.
When I use old iPhone 5S, there is no problem.
There is only one difference regarding the BT between 5S and 6S - 5S uses older 4.0 version of BT instead of 4.2 version on 6S.
Dont know what other things to try 😟