I enabled the service for my display and also set the preset. Behaviour is very random. Sometimes, VNC Service starts at reboot, sometimes not.
systemctl enable vncserver@:1.service
systemctl start vncserver@:1.service
Typically you will want to check the journal for more details on that particular service. I've seen in the past that configurations for units not checking for appropriate states or other services can lead to unit start failures.
One common problem is the network state. If the log for the unit shows that it failed to connect due to networking states, this may be worth looking into.
Any other issues outlined in the logs that result in the service failing to start or to stay on would be the starting point for further review.