Phone call not using Bluetooth

[jan2]

I have a Nokia 6 (2017) with Android 8.1.
The phone is paired with the Cardo SmartH helmet headset.
I can use the headset to listen to music, use the Google Assistant, so no problem for the audio connection. However when I place or receive a phone call, the phone is using the internal speaker.
I can see the Bluetooth option selected at the start of the call, but it switches automatically to phone. I can select the output back to Bluetooth, but again it switches back to the internal speaker.

I tried it on another Nokia 6, with the same result.
I have reset network connections, switched off WiFi, deleted and paired the headset again, rebooted my phone and headset.

I tried it on a Windows phone and that worked without issues.

Any suggestions?

Thanks,

Jan

 

[jan2]

Nobody? I added some screenshots to clarify.

 

[mikedt]

If it's 2 Nokias both with same problem, and you've tried resetting etc., it sounds it could be buggy firmware. Which is something that only Nokia can fix and help with. I think it should work, but it seems like there's an issue with the Nokia phones, that Nokia needs to address.

 

[chanchan05]

Have you looked into bluetooth settings and set it to use for call audio?

 

[jan2]

Yes , the option is checked. Otherwise I wouldn't have the Bluetooth sound option in the Phone App.
In this screenshot you can see that I can select the Bluetooth sound option, but it immediately goes back to the Phone sound option.
If the call starts, you also see the Bluetooth sound option selected, but then again it goes immediately to Phone sound option.

 

[tabtan]

Software for my mobile

 

[jan2]

I have installed the latest beta version of the Google phone app, but still the same result.