Also seeing this in a ceph job in n-api:

https://d494348350733031166c-4e71828f84900af50a9a26357b84a827.ssl.cf1.rackcdn.com/689842/5/check/devstack-plugin-ceph-tempest/962455b/controller/logs/screen-n-api.txt.gz

Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi [None req-a94464d7-d36c-405f-a42f-344e543cb205 tempest-TestShelveInstance-198061268 tempest-TestShelveInstance-198061268] Unexpected exception in API method: NovaException: Cell 901092b8-6de2-4aad-b21a-e1c21691eb30 is not responding and hence instance info is not available.
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi Traceback (most recent call last):
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi   File "/opt/stack/nova/nova/api/openstack/wsgi.py", line 671, in wrapped
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi     return f(*args, **kwargs)
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi   File "/opt/stack/nova/nova/api/openstack/compute/servers.py", line 471, in show
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi     cell_down_support=cell_down_support)
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi   File "/opt/stack/nova/nova/api/openstack/compute/servers.py", line 374, in _get_server
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi     cell_down_support=cell_down_support)
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi   File "/opt/stack/nova/nova/api/openstack/common.py", line 472, in get_instance
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi     cell_down_support=cell_down_support)
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi   File "/opt/stack/nova/nova/compute/api.py", line 2605, in get
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi     expected_attrs, cell_down_support=cell_down_support)
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi   File "/opt/stack/nova/nova/compute/api.py", line 2552, in _get_instance
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi     expected_attrs, cell_down_support)
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi   File "/opt/stack/nova/nova/compute/api.py", line 2545, in _get_instance_from_cell
Oct 21 22:41:11.686000 ubuntu-bionic-ovh-gra1-0012414214 <email address hidden>[20043]: ERROR nova.api.openstack.wsgi     "info is not available.") % cell_uuid)