The following procedure should ensure to re-create the uuid of the NoMachine installation, it can be helpful when the installation is cloned to another machine:

sudo /usr/NX/bin/nxserver --shutdown

sudo mv /usr/NX/etc/uuid /usr/NX/etc/uuid.bck

sudo /usr/NX/bin/nxserver --startup

At startaup, instead, the nxnode service is no longer enabled:

$ sudo /usr/NX/bin/nxserver --startup
NX> 111 New connections to NoMachine server are enabled.
NX> 161 Enabled service: nxserver.
NX> 162 Disabled service: nxnode.
NX> 161 Enabled service: nxd.

and users cannot connect to the remote desktop.

Restoring the original uuid, uuid.bck, and then executing 'nxserver --startup' makes the node working again.