The logs don’t seem to contain any problem related to starting virtual sessions. Can you make sure you follow the steps here: https://www.nomachine.com/AR07K00677 in the section dedicated to Linux.
You will need to:
1) Set log level to debug as per instructions
2) Reproduce the problem.
3) Create a compressed archive of the NoMachine /var/log directory.
4) Send the archive to NoMachine Support Team by e-mail .
Don’t forget to include the client side logs as well. The userhome/.xsession-errors file will be useful to. Send everything to issues[at]nomachine.com.