Hello dtc42,
I logs you submitted we found that session because nxserver choose wrong X server to attach to. In user processes we can found two running X servers:
vnc4 Xvnc4 :1 -desktop localhost:1 (googlestudent) -auth /home/googlestudent/.Xauthority -geometry 1280×1024 -depth 16 -rfbwait 30000 -rfbauth /home/googlestudent/.vnc/passwd -rfbport 5901 -pn -fp /usr/X11R6/lib/X11/fonts/Type1/,/usr/X11R6/lib/X11/fonts/Speedo/,/usr/X11R6/lib/X11/fonts/misc/,/usr/X11R6/lib/X11/fonts/75dpi/,/usr/X11R6/lib/X11/fonts/100dpi/,/usr/share/fonts/X11/misc/,/usr/share/fonts/X11/Type1/,/usr/share/fonts/X11/75dpi/,/usr/share/fonts/X11/100dpi/ -co /etc/X11/rgb
and
Xvfb Xvfb :0 -auth /home/googlestudent/Xvfb-0.auth -screen 0 1280x1024x2
Please try to disable other X server before connecting to session or uncomment in node.cfg file key:
#
# Specify on which physical display the server must connect.
#
#DisplayDefault :0
Then nxserver will always choose X server with display defined in this key.