Okay, I have set up the debug level repeated the troublesome connections and saved all the logs. I had to delete some records from the middle of the Darcymain nxerror.log to keep everything under 1024Kb. The deleted records were highly redundant and during times NoMachine was not in use. I can send the full log if it is necessary.
Today, unlike yesterday I could see the desktop of the Ubuntu PCs but still had no control.
I’ll check back to see if you need something else.