I started to detail my difficulty and had included all of the usual version information about my setup, but my system had to be restarted, and I lost the details that I entered here. However, I suspect that my problem may affect many people with quite different setups. I have four monitors connected to my linux server computer. When I connect to this system with a linux portable everything seems to work as it should, except:
WARNING! If you have a multi monitor server, do not select “resize remote screen” on the NoMachine client while you are displaying all the monitors. In my case, at least, it changes the relative resolutions and positions of the layout of the monitors on the server so that they overlap–a mess that required a trip to NVIDIA X Server Settings to set right again. That was no simple matter, since it reversed the display of my main monitor, showing a left to right mirror image. I had to restart the system to return to normal.
I am not criticizing NoMachine. I think we may have a logical problem that will be impossible to fix.
Consequently, if the problem is reproducible on other systems, it might be well to warn users in the documentation.