We got your screenshot and are investigating. Can you send us logs (of the problematic session) and also tell us if you have lightweight mode enabled on the server. You can check this by:
– open the NoMachine GUI from the Programs/Applications menu
– click on the last icon ‘Preferences’
– select ‘Server status’
– select ‘Server preferences’
– select ‘Performances’
– check the box ‘Use lightweight mode in virtual sessions’