@Jenkler I wouldn't have thought to do that. But now using either the default theme or the Slick theme it is all displaying as it should. The error was when using the nodebb-theme-material-revisit theme.
@Joykiller there is no issue setting NodeBB up as root. I always do it like that and later chown the installation to another user. Then I start NodeBB over Supervisoe from that non-root user.
Update:
All issues resolved. 😛
Re-setup everything.