When "joinUnassigned=false" in Description.ext, the Headless client is rendered objNull in mission.
Cannot see that in Briefing screen. I need to input the name of the Headless client on the debug console to see that it is non existent object. Of course as a result, anything associated with the Headless client does not execute.

When the above command is commented out or is joinUnassigned=true then all is functioning normally.