Many thanks. I added the -proposed repo and upgraded. I think this probably fixed a bunch of things so a bit hard to disentangle. Now running openvswitch 2.13.3-0ubuntu0.20.04.1.

With some repeated reboots I sometimes still end up with log full of these messages;

2021-04-23T13:14:42.868Z|00001|vlog|INFO|opened log file /var/log/ovn/ovn-controller.log
2021-04-23T13:14:42.872Z|00002|reconnect|INFO|unix:/var/run/openvswitch/db.sock: connecting...
2021-04-23T13:14:42.872Z|00003|reconnect|INFO|unix:/var/run/openvswitch/db.sock: connected
2021-04-23T13:14:42.875Z|00004|main|INFO|OVS IDL reconnected, force recompute.
2021-04-23T13:14:42.877Z|00005|reconnect|INFO|ssl:10.23.129.156:6642: connecting...
2021-04-23T13:14:42.877Z|00006|main|INFO|OVNSB IDL reconnected, force recompute.
2021-04-23T13:14:42.883Z|00007|reconnect|INFO|ssl:10.23.129.156:6642: connected
2021-04-23T13:14:42.886Z|00008|ofctrl|INFO|unix:/var/run/openvswitch/br-int.mgmt: connecting to switch
2021-04-23T13:14:42.886Z|00009|rconn|INFO|unix:/var/run/openvswitch/br-int.mgmt: connecting...
2021-04-23T13:14:42.887Z|00010|rconn|INFO|unix:/var/run/openvswitch/br-int.mgmt: connected
2021-04-23T13:14:42.887Z|00011|ovsdb_idl|WARN|transaction error: {"details":"RBAC rules for client \"juju-3eccf9-2-lxd-3\" role \"ovn-controller\" prohibit row insertion into table \"Chassis\".","error":"permission error"}
2021-04-23T13:14:42.888Z|00012|main|INFO|OVNSB commit failed, force recompute next time.
2021-04-23T13:14:42.888Z|00001|pinctrl(ovn_pinctrl2)|INFO|unix:/var/run/openvswitch/br-int.mgmt: connecting to switch
2021-04-23T13:14:42.888Z|00002|rconn(ovn_pinctrl2)|INFO|unix:/var/run/openvswitch/br-int.mgmt: connecting...
2021-04-23T13:14:42.890Z|00013|ovsdb_idl|WARN|transaction error: {"details":"RBAC rules for client \"juju-3eccf9-2-lxd-3\" role \"ovn-controller\" prohibit row insertion into table \"Chassis\".","error":"permission error"}
2021-04-23T13:14:42.890Z|00014|main|INFO|OVNSB commit failed, force recompute next time.
2021-04-23T13:14:42.890Z|00003|rconn(ovn_pinctrl2)|INFO|unix:/var/run/openvswitch/br-int.mgmt: connected
2021-04-23T13:14:42.891Z|00015|ovsdb_idl|WARN|transaction error: {"details":"RBAC rules for client \"juju-3eccf9-2-lxd-3\" role \"ovn-controller\" prohibit row insertion into table \"Chassis\".","error":"permission error"}
2021-04-23T13:14:42.892Z|00016|main|INFO|OVNSB commit failed, force recompute next time.
2021-04-23T13:14:42.892Z|00017|binding|INFO|Claiming lport bdc6da30-c675-4c3f-a0ee-870c8074fb0a for this chassis.
2021-04-23T13:14:42.892Z|00018|binding|INFO|bdc6da30-c675-4c3f-a0ee-870c8074fb0a: Claiming fa:16:3e:4d:10:97 fc00:69f7:40ec:ade7:f816:3eff:fe4d:1097
2021-04-23T13:14:42.892Z|00019|binding|INFO|bdc6da30-c675-4c3f-a0ee-870c8074fb0a: Claiming unknown
2021-04-23T13:14:42.892Z|00020|ovsdb_idl|WARN|transaction error: {"details":"RBAC rules for client \"juju-3eccf9-2-lxd-3\" role \"ovn-controller\" prohibit row insertion into table \"Chassis\".","error":"permission error"}
2021-04-23T13:14:42.892Z|00021|main|INFO|OVNSB commit failed, force recompute next time.
2021-04-23T13:14:42.896Z|00022|binding|INFO|Claiming lport bdc6da30-c675-4c3f-a0ee-870c8074fb0a for this chassis.
2021-04-23T13:14:42.896Z|00023|binding|INFO|bdc6da30-c675-4c3f-a0ee-870c8074fb0a: Claiming fa:16:3e:4d:10:97 fc00:69f7:40ec:ade7:f816:3eff:fe4d:1097
2021-04-23T13:14:42.896Z|00024|binding|INFO|bdc6da30-c675-4c3f-a0ee-870c8074fb0a: Claiming unknown
...