'bro': No such device

I installed a fresh OpenNebula 5.12.0.3 and on another server I installed Ubuntu 20.04 as a node for it. That node has issues running VMs. If trying a manual start we see this:

oneadmin@ou-devcre-01: ~/datastores/0/37$ virsh create deployment.0
error: Failed to create domain from deployment.0
error: Cannot get interface MTU on ‘br0’: No such device

I enabled some logs for networkd-dispatcher, so the log is quite messy now, but here’s the syslog when I try to launch it:
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: DEBUG:Signal: typ=dbus.String(‘org.freedesktop.network1.Link’), data=dbus.Dictionary({dbus.String(‘CarrierState’): dbus.String(‘off’, variant_level=1), dbus.String(‘OperationalState’): dbus.String(‘off’, variant_level=1)}, signature=dbus.Signature(‘sv’)), path=dbus.ObjectPath(’/org/freedesktop/network1/link/_321’)
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: WARNING:Unknown index 21 seen, reloading interface list
Mar 25 11:38:03 ou-devcre-01 systemd-udevd[44712]: Using default interface naming scheme ‘v245’.
Mar 25 11:38:03 ou-devcre-01 systemd-udevd[44712]: ethtool: autonegotiation is unset or enabled, the speed and duplex are not writable.
Mar 25 11:38:03 ou-devcre-01 dnsmasq[20919]: reading /etc/resolv.conf
Mar 25 11:38:03 ou-devcre-01 dnsmasq[20919]: using nameserver 127.0.0.53#53
Mar 25 11:38:03 ou-devcre-01 dnsmasq[20919]: reading /etc/resolv.conf
Mar 25 11:38:03 ou-devcre-01 dnsmasq[20919]: using nameserver 127.0.0.53#53
Mar 25 11:38:03 ou-devcre-01 libvirtd[31045]: Cannot get interface MTU on ‘br0’: No such device
Mar 25 11:38:03 ou-devcre-01 dnsmasq[20919]: reading /etc/resolv.conf
Mar 25 11:38:03 ou-devcre-01 dnsmasq[20919]: using nameserver 127.0.0.53#53
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: DEBUG:Performed interface scan; state: <Dispatcher({‘script_dir’: ‘/etc/networkd-dispatcher:/usr/lib/networkd-dispatcher’})>
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: ERROR:Unknown interface index 21 seen even after reload
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: DEBUG:Signal: typ=dbus.String(‘org.freedesktop.network1.Link’), data=dbus.Dictionary({dbus.String(‘AdministrativeState’): dbus.String(‘linger’, variant_level=1)}, signature=dbus.Signature(‘sv’)), path=dbus.ObjectPath(’/org/freedesktop/network1/link/_321’)
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: WARNING:Unknown index 21 seen, reloading interface list
Mar 25 11:38:03 ou-devcre-01 libvirtd[31045]: Failed to open file ‘/sys/class/net/one-37-0/operstate’: No such file or directory
Mar 25 11:38:03 ou-devcre-01 libvirtd[31045]: unable to read: /sys/class/net/one-37-0/operstate: No such file or directory
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: DEBUG:Performed interface scan; state: <Dispatcher({‘script_dir’: ‘/etc/networkd-dispatcher:/usr/lib/networkd-dispatcher’})>
Mar 25 11:38:03 ou-devcre-01 networkd-dispatcher[39151]: ERROR:Unknown interface index 21 seen even after reload

I’m guessing that the error about Unknown interface index 21 seen even after reload is the culprit so that br0 isn’t created on the fly as it should.

Does anyone have ideas why the interface index gets messed up?