I'm not sure I know enough to troubleshoot, but I can post what is working for me.
For the extender:
Mode = MC
Ifc = Network
Network Mode = DHCP on,
Role = Slave
Port 5004.
In the GUI config window: enable for WDL (and the applicable mix window), rtpMidi, the MCU-ext.xml template, and entered the IP address for the extender.
It normally takes about 10 seconds after I hit OK in the config window before everything syncs up and the "wait" message goes away. The scribble strips are initially blank, but if I change the mix, then everything populates. I'm using a version (10.5) of the GUI prior to the buttons lighting up and colors in the scribble strips.