This also seem to be the exact same issue :
https://ask.openstack.org/en/question/121209/external-network-with-more-than-one-vlan-not-working-in-stein-release/
This also seem to be the exact same issue :
https:/ /ask.openstack. org/en/ question/ 121209/ external- network- with-more- than-one- vlan-not- working- in-stein- release/