Bluetooth and Radiosat (Renault handsfree set): regression in connection

REPRODUCIBILITY (% or how often): 50%
BUILD ID = OS VERSION (Settings > About product): 3.4.0.24
HARDWARE (Jolla1, Tablet, XA2,…): Xperia X
UI LANGUAGE: German
REGRESSION: (compared to previous public release: Yes, No, ?): Yes

DESCRIPTION:

After the latest update (3.4.0.24) the connection with my handsfree set (Renault Radiosat) got much worse. It was already buggy before. This didn’t get any better.

But now also the phone connection is broken. The phone connects in most cases (and e.g. shows the symbol for connection quality of the mobile connection of the phone). It’s also possible to select a contact in the car (which wouldn’t be the case, if there was no connection at all), but I can’t dial a number. Nothing happens, when I click on a contact in the handsfree set.

Also incoming calls don’t get forwarded to the handsfree set. The phone is ringing instead of the handsfree set.

It seems that pulseaudio is in a more broken state than before and audiorouting issues are not only affecting media streams but also phone streams.

I tried to reconnect the phone with the handsfree set, but I didn’t manage to achieve this yet. Maybe this is also broken.
I deleted the content of /var/lib/bluetooth and deleted all devices on the Radiosat. They are not able to find each other anymore.

PRECONDITIONS:

Xperia X with 3.4.0.24, Renault Scenic III with Radiosat

STEPS TO REPRODUCE:

  1. Have phone and carkit connected
  2. try to make a phone call
    or
  3. try to pickup a phone call

EXPECTED RESULT:

be able to make and receive phone calls via handsfree set in 95% of the time.

ACTUAL RESULT:

It’s not possible to start a phonecall

ADDITIONAL INFORMATION:

What would be relevant here? How do I debug the bluetooth connection or the pulseaudio routing?