bluetoothctl does not find BLE device with ControllerMode = dual

Hello,

I bought an HiFi amplifier NAD C368 and am running Kodi on a Lubuntu System. The NAD C368 uses a bluetooth low energy (BLE) adapter to use it as an audio sink or to control all features of the amp via a smartphone app (NAD Remote App).

I am able to pair with the NAD Amp using my smartphone but not using Lubuntu and bluetoothctl within it.

I was not able to the the device after scan with the default configuration of ControllerMode = dual. But when I set ControllerMode explicit to LE in /etc/bluetooth/main.conf the device is listed. I think, this is a bug.

Further: When I then try to pair the device I get Authentication Error. Any idea what the root problem is?

I have posted the question in other forums but there is none who has answered. So I hope I find someone here.

Distributor ID: Ubuntu
Description: Ubuntu 20.04.3 LTS
Release: 20.04
Codename: focal

Lubuntu 20.04 (Linux K700 5.4.0-88-generic #99-Ubuntu SMP Thu Sep 23 17:29:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux)
bluetoothctl 5.49

If of interest, I have done a monitoring with BTMON and I have stored the output.

Regards