Hands-free kit not working properly FORD FOCUS

Every time I get an income call or I like to call someone, the car automatically switch in private mode, which means you can not hear anything what people say and people can not hear you. Disable the private mode (at the car) manually does not seem to change anything. At the phone (Dialer App) you can not choose the proper speaker which would be the bluetooth speaker of the car (the button is shown greyed).
It only appears when using the Ubuntu Phone (it has been tested with an Android phone where it works).

Surprisingly sometimes it works instantly, even through the right speakers, but most of the time it does not.

Thus, I would like to point out that the phone is connected via bluetooth the whole time without any connectivity problems.

Naturally I would like that calling/receiving calls work properly, without hassle.

Car: FORD FOCUS
Ubuntu Phone: BQ Aquaris E5
OTA: 10.1