check with the Security Group if there is a rule to open port 4000 and SSH port.
Perhaps you deleted it by accident.
Are you connecting to NoMachine through the NX protocol or the SSH protocol?
Check Nomachine status with command „/ usr / NX / bin / nxserver –status”
You should see
NX> 111 New connections to NoMachine server are enabled.
NX> 161 Enabled service: nxserver.
NX> 161 Enabled service: nxnode.
NX> 161 Enabled service: nxd.
I understand this is a VM which has been working for a while and was previously accessed via NoMachine?