Comment 3 for bug 2038978

FYI, anyone that is running into this, the temporary workaround which restored connectivity was:

# find the NAT mapping for the FIP that is _outside_ the external gw subnet
$ ovn-nbctl find NAT external_ip=X.Y.Z.158
_uuid : 3935eb7d-dee9-4e6f-b645-f43c9fe441ff
allowed_ext_ips : []
exempted_ext_ips : []
external_ids : {"neutron:fip_external_mac"="fa:16:3e:ff:88:8a", "neutron:fip_id"="1c37787b-0b47-4802-93bc-58bccd5fb731", "neutron:fip_network_id"="7abff1a9-a103-46d0-979a-1f1e599f4f41", "neutron:fip_port_id"="d060e81c-6e7e-4d5a-b0ba-81d550193d02", "neutron:revision_number"="234", "neutron:router_name"=neutron-b97179c7-abe4-4e28-908b-952ff8abd8c4}
external_ip : "X.Y.Z.158"
external_mac : "fa:16:3e:ff:88:8a"
external_port_range : ""
gateway_port : []
logical_ip : "192.168.240.166"
logical_port : "d060e81c-6e7e-4d5a-b0ba-81d550193d02"
options : {}
type : dnat_and_snat

# enable options:add_route
$ ovn-nbctl set nat 3935eb7d-dee9-4e6f-b645-f43c9fe441ff options:add_route="true"

Upon doing this, connectivity was restored!