Comment 2 for bug 1752986

This is a bit of a stretch, but if you're consuming notifications on the rpc queue, you could maybe figure out at what point the task_state on that given instance is getting set to None because it's not obvious to me where the task_state gets set to None while an instance is being live migrated.

https://docs.openstack.org/nova/latest/configuration/config.html#notifications.notify_on_state_change