Comment 1 for bug 1808171

so just loking at the logs around when processing of the port was skipped in the neutron agent we see

that the vms tap interface tap472ab433-bc corresponding to port 472ab433-bc18-41b5-85ae-009611117b70
is present in the db list at http://logs.openstack.org/46/623246/3/check/nova-multiattach/efa830b/logs/screen-q-agt.txt.gz#_Dec_11_23_56_12_715432

Dec 11 23:56:12.715432 ubuntu-xenial-inap-mtl01-0001136812 neutron-openvswitch-agent[21879]: DEBUG ovsdbapp.backend.ovs_idl.transaction [-] Running txn n=1 command(idx=0): DbListCommand(if_exists=True, records=[u'tap6b476c8d-35', u'tap459d08b5-8c', u'tapc4cbed6d-26', u'int-br-ex', u'tap9596db0a-58', u'tapd2e38552-81', u'qr-6ffb4153-0f', u'qg-89b08004-24', u'tap467f555d-fd', u'tap45563a2d-cd', u'qg-88ca1551-8f', u'tap5a8d8e13-3d', u'qr-35a687f0-fb', u'qg-c992632f-da', u'tapf2f4235b-c3', u'tap727b1a5d-e7', u'qg-a51133f8-41', u'tapd883b80b-39', u'tap8c3289ef-07', u'qr-c64db2ce-aa', u'tapb734a414-18', u'tapbc284b29-92', u'qr-3a500395-7f', u'patch-tun', u'tap472ab433-bc'], table=Interface, columns=['name', 'external_ids', 'ofport'], row=False) {{(pid=21879) do_commit /usr/local/lib/python2.7/dist-packages/ovsdbapp/backend/ovs_idl/transaction.py:84}}

then there is a warningn

ubuntu-xenial-inap-mtl01-0001136812 neutron-openvswitch-agent[21879]: WARNING neutron.agent.common.ovs_lib [None req-cc26f856-2521-411e-ae10-34ad96b7c665 None None] ofport: [] for VIF: 472ab433-bc18-41b5-85ae-009611117b70 is not a positive integer: OVSFWTagNotFound: Cannot get tag for port tap5b6aa631-3b from its other_config: {}

and then the message saying the port was not found

Dec 11 23:56:12.725010 ubuntu-xenial-inap-mtl01-0001136812 neutron-openvswitch-agent[21879]: INFO neutron.plugins.ml2.drivers.openvswitch.agent.ovs_neutron_agent [None req-cc26f856-2521-411e-ae10-34ad96b7c665 None None] Port 472ab433-bc18-41b5-85ae-009611117b70 was not found on the integration bridge and will therefore not be processed

now the stagege thing about the warining is that the tap listed is wrong.
the warning states "OVSFWTagNotFound: Cannot get tag for port tap5b6aa631-3b from its other_config: {}" however the tap should be tap472ab433-bc