Comment 1 for bug 1774363

Everything goes through nova-conductor for database updates so if that's down, you have problems. You can reset the state of the instance using the reset state API (as admin):

https://docs.openstack.org/python-openstackclient/latest/cli/command-objects/server.html#server-set

nova server set --state error

Although you can't unshelve from that if the instance is really offloaded and not on a host. If the shelve offload image snapshot was successful, then you basically need to delete the old server and create a new one from the shelved offloaded image snapshot.