If I restore the NM Viewer window after some period it was minimized, it shows just a small noisy frame instead of remote desktop.
Local machine: W11, Iris Xe Graphics, 2560×1600, latest NM 8x (same was for latest NM 7x);
Remote desktop: CentOS7, Mate, 2560×1440, latest NM 7x.
I use “full screen” mode without changing remote desktop resolution, so having black stripes at top and bottom.
On a screenshot nomachine_OK – top right corner of my display showing remote display.
On a screenshot nomachine_notOK – same region captured with improper behaviour I mentioned above.