Here some related bug reports:
- Suddenly no incoming voice then using car kit
- Broken pairing, no connection with Bluetooth car kit [10 III, 4.4.0.68]
- VoLTE, incoming call kills bluetooth connection to car kit, hangs up on caller and can't be picked by car kit at second attempt
- Bluetooth connection to car does not work. Music is not sent to car by time to time and I can't voice during a phone call
- Call audio keeps routing back to Bluetooth