Since the ovn-controller clearly has the correct notion of its FQDN I think this points in the direction of Octavia charm having the wrong information about what hostname to use.

Looking at the `ovsdb-subordinate` interface code it does set the `available` state prior to having published anything which may lead this part of the Octavia charm code create a port with a shortname:
https://github.com/openstack/charm-octavia/blob/b6bdb1a12cb946ceabf73f078d5791072d513507/src/reactive/octavia_handlers.py#L142-L150

Previously the charm would self-heal/paper over this during a update-status hook but as we have started to (rightfully) disable charm processing during update-status hook this no longer happens.

So I guess a viable path to fix this specific issue would be:
1) Fix the `ovsdb-subordinate` interface code so that it does not set `avaialble` state until chassis name is available on the relation.
2) Change the octavia charm behaviour when it finds its port down after initial creation. In addition to log the event we could put the charm into a `waiting` or`blocked` state and possibly do some waiting for it to come up.

Looking at the hook execution history in the log on the failed units support this:
2020-10-20 10:37:47 INFO juju-log toggling port 21b287ea-4595-441c-9915-1f2eef110670 (admin_state_up: False status: DOWN)
2020-10-20 10:39:06 INFO juju-log Reactive main running for hook update-status
2020-10-20 10:43:34 INFO juju-log Reactive main running for hook update-status
2020-10-20 10:48:56 INFO juju-log Reactive main running for hook update-status
2020-10-20 10:53:08 INFO juju-log Reactive main running for hook update-status
2020-10-20 10:57:51 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:03:41 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:10:03 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:14:25 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:19:47 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:25:16 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:29:18 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:35:04 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:40:48 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:46:08 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:50:21 INFO juju-log Reactive main running for hook update-status
2020-10-20 11:55:49 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:00:21 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:04:39 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:09:48 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:13:57 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:19:39 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:25:37 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:31:27 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:36:22 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:41:54 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:47:41 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:53:33 INFO juju-log Reactive main running for hook update-status
2020-10-20 12:57:44 INFO juju-log Reactive main running for hook update-status
2020-10-20 13:02:55 INFO juju-log Reactive main running for hook update-status
2020-10-20 13:08:54 INFO juju-log Reactive main running for hook update-status
2020-10-20 13:14:25 INFO juju-log Reactive main running for hook update-status
2020-10-20 13:19:20 INFO juju-log Reactive main running for hook update-status
2020-10-20 13:23:42 INFO juju-log Reactive main running for hook update-status