Could you please specify if the session is interrupted by screensaver (so the screen goes black and after slight movement of mouse or keyboard it returns) or by screen lock (session is locked and the password must be entered again to unlock it)? Secondly, could you please tell us what are your screensaver and energy settings?
To do so please, while inside the NX session, open K menu and click “System Settings” (If the icon is not visible right away, type System Settings in the search bar). Then click “Power Management” and please tell us what is set under “Dim Display” and “Suspend Session”. The “Button events handling” section may also be interresting.
Then please go back to “System Settings” and go to “Display and Monitor” -> “Screen Saver” and please share what’s set in the “Settings” section. So which options are checked and what are their values.