VRDE not working on VirtualBox 6.0.12/Debian buster

[emfau]

Hi,

I am having trouble to get VRDE working after upgrading to debian buster and virtualbox 6.0.12.

$ dpkg -l | grep -i virtualbox
ii  virtualbox-6.0                 6.0.12-133076~Ubuntu~bionic  amd64        Oracle VM VirtualBox

I installed Oracle Extension Pack as required for VRDE.

$ vboxmanage list -l extpacks
Extension Packs: 1
Pack no. 0:   Oracle VM VirtualBox Extension Pack
Version:      6.0.12
Revision:     133076
Edition:      
Description:  USB 2.0 and USB 3.0 Host Controller, Host Webcam, VirtualBox RDP, PXE ROM, Disk Encryption, NVMe.
VRDE Module:  VBoxVRDP
Usable:       true 
Why unusable:

VM configuration shows:

$ vboxmanage showvminfo <vmname> | grep -i vrde
VRDE:                        enabled (Address 127.0.0.1, Ports 55999, MultiConn: off, ReuseSingleConn: off, Authentication type: null)

When starting the VM unfortunately no listener is started on 55999. The log shows:

00:00:00.098441 Installed Extension Packs:
00:00:00.098463   Oracle VM VirtualBox Extension Pack (Version: 6.0.12 r133076; VRDE Module: VBoxVRDP)
00:00:00.099904 Console: Machine state changed to 'Starting'
00:00:00.116128 VRDE: VirtualBox Remote Desktop Extension is not available.

I tried all I found in other threads, like reinstalling Virtualbox and Extensions multiple times, rebooting the VM Host - but to no avail.

Any idea how to resolve the situation?

Thanks for your time!