Comment 5 for bug 1906683

From the log which You sent it seems that neutron server already sent to nova notification:

2020-12-03 13:13:20.928 21 INFO neutron.notifiers.nova [-] Nova event response: {'name': 'network-changed', 'server_uuid': '04b615d1-e911-48f9-bdb1-cf950ec49ef2', 'tag': '1c8b47f1-417f-489c-851c-6c0324d33530', 'status': 'completed', 'code': 200}

I think You should check check on nova's side where this notification is.
And also, can You check if port for which nova waits is really UP or DOWN just before nova fails instance?