Alright, as I couldn't find a bug reporting this situation - I have opened bug 1534270.
Also I had to tweak my SELinux in order to be able to start the service ... Anyone else observing this behaviour ?
Issues related to applications and software problems
TrevorH wrote:It appears to be a bug that's fixed by editing /etc/systemd/system/vncserver@:1.service (or whatever file you use) and in the [Service] section, right after where it currently has "User=youruser" add the line
Save and exit the file, run systemctl daemon-reload and then systemctl restart vncserver@:1 and log back in and it should work.
Thank you TrevorH! Fixed it for my CentOS 7.4