xrdp connect to the same session

Better yet, set your /etc/xrdp/xrdp.ini thusly:

[xrdp1]name=sesman-Xvnclib=libvnc.sousername=askpassword=askip=127.0.0.1port=ask5910

This way it asks for the port with a default of 5910. If no vnc session exists on 5910 then a 5910connection attempt will fail. In that case try again, but set the port to -1 to force the creation of a new session, typically on 5910.