Problem solved. Reason was a fail at engine-setup.
Engine setup showed cluster not in Global Maintenance mode, even if the cluster was indeed
in Global Maintenance. Had to force engine setup by using a hint from
https://www.ovirt.org/media/Hosted-Engine-4.3-deep-dive.pdf, Major issues 4.
After this, I hit the "internal server error" problem, which I solved by
downgrading postgresql-jdbc:
$ dnf downgrade postgresql-jdbc
$ systemctl restart ovirt-engine