Comment 4 for bug 2078845

The "Cannot find Logical_Router_Port" exception is logged when you add a subnet to a router, unrelated to vpnaas, e.g. with the following steps

openstack router create routername
openstack network create networkname
openstack subnet create subnetname --network networkname --subnet-range 192.168.22.0/24
openstack router add subnet routername subnetname

Internally during the creation of a vpn service the ovn variant of the plugin will create some transit network and subnet and add it to the router. That's when the exception is logged for an internal port with IP 169.254.0.1.
As mentioned earlier, this exception doesn't break the vpn setup.