Recently while setting up a new Ubuntu 20.04 VM (from the Quick Create in Hyper-V) I found that I could not RDP into the machine once it was setup, however it was sitting on my network configured with my NAT Switch.
Turns out that the xrdp daemon was not starting and had a cryptic error about VSOCK. Doing a bit of research found that I needed to edit the /etc/xrdp/xrdp.ini file and set the option use_vsock from true to false
#/etc/xrdp/xrdp.ini
use_vsock=false
After that change I restarted the xrdp daemon and was able to connect to it.