You say that you think the problem is on the client side, so with the Mac computer. Have you tried connecting from a different computer and/or with a different OS? This is the easiest way to know if the problem is being triggered on the client side.
You can also look in the crashes list on your Mac. In a terminal run:
ls -ltr ~/Library/Logs/DiagnosticReports/
If something is happening in nxplayer, it will be reported there.
Another thing to consider is that you need xquartz installed on the Mac in order to be able to run custom sessions/rootless sessions. Are you trying to run a “custom virtual desktop session”? See here for a quick reference:
How to run a single Linux application with NoMachine client on macOS
https://knowledgebase.nomachine.com/AR07K00675
but you can search “xquartz” in these forums as well. What happens if you try to start a new virtual desktop (full desktop, not custom)?
Failing those suggestions, then we need to look also on the server side.
What’s the Linux distribution and its version where you have installed the NoMachine server?
What NoMachine product is installed on the Linux host?
You say “open the virtual desktop”, is this a virtual desktop which you are reconnecting to? What desktop environment (DE) is it? Gnome, KDE, something else? If it is a virtual desktop already running (i.e it’s not new), what applications do you have open there? Have you noticed if this happens when you have specific program open/running in the desktop?
What happens if you open a new virtual desktop with same DE and with a different DE?