@tosigus: What do you mean with “When non NoMachine Tray Icon”? Have you changed the “Hide the NoMachine icon in system tray” option?
No.
The tray icon should be always visible while somebody connects or disconnects. Does the CPU have spikes while the icon is visible at connection and at disconnection?
Yes.
First connection after reboot before = no Icon, no high CPU.
Then logout = no Icon, high CPU.
Sometimes first login after reboot, no Icon shows up (no high CPU), after some time the Icon comes up (high CPU).