Comment 8 for bug 1738373

My latest comment references https://bugs.launchpad.net/nova/+bug/1809136, which is a very similar bug, with error message "Unsupported VIF type unbound convert '_nova_to_osvif_vif_unbound'"

After checking, my rocky (not stein!) nova-compute containers weren't running with the fix mentioned in the relevant launchpad (https://opendev.org/openstack/nova/commit/7b4f5725f821ef89176ef69f036471eaaf8a6201), so once I updated it manually with the fix, after a reboot the issue stopped occurring. :-)