taking a look closer, this could have happened since the neutron-gateway (server side) had an older version that is not aware of 1.5 objects, while neutron-ovs-agent (client side) requested a 1.5 versioned object, the backwards compatibility layer is meant to be used the other way around where the server is aware of newer versions while the client is not, so the server can remove fields from the response to downgrade the object and hand back a compatible one.
taking a look closer, this could have happened since the neutron-gateway (server side) had an older version that is not aware of 1.5 objects, while neutron-ovs-agent (client side) requested a 1.5 versioned object, the backwards compatibility layer is meant to be used the other way around where the server is aware of newer versions while the client is not, so the server can remove fields from the response to downgrade the object and hand back a compatible one.