FWIW I can reproduce this artificially in devstack by manually removing the associated volume secret:

$ sudo virsh secret-list
 UUID                                  Usage
--------------------------------------------------------------------------------
 6713c0d1-7c30-4546-bbcf-c60ee9fcb9f4  volume ba7486b3-4ea5-4715-89f3-1ec86b0d9812
 e4897c8d-b271-44e8-b366-367ecddb8a3d  ceph client.cinder secret

$ nova stop test
Request to stop server test has been accepted.

$ virsh secret-undefine 6713c0d1-7c30-4546-bbcf-c60ee9fcb9f4

$ nova start test

$ journalctl -u devstack@n-*
[..]
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 2895, in start_instance
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     self._power_on(context, instance)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 2865, in _power_on
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     block_device_info)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 2992, in power_on
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     self._hard_reboot(context, instance, network_info, block_device_info)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 2839, in _hard_reboot
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     block_device_info=block_device_info)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 1047, in destroy
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     destroy_disks)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 1132, in cleanup
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     instance=instance)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 220, in __exit__
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     self.force_reraise()
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 196, in force_reraise
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     six.reraise(self.type_, self.value, self.tb)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 1119, in cleanup
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     self._disconnect_volume(context, connection_info, instance)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 1345, in _disconnect_volume
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     self._detach_encryptor(context, connection_info, encryption=encryption)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 1460, in _detach_encryptor
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     encryption)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 1381, in _get_volume_encryptor
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     **encryption)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/os_brick/encryptors/__init__.py", line 91, in get_volume_encryptor
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     **kwargs)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_utils/importutils.py", line 44, in import_object
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     return import_class(import_str)(*args, **kwargs)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/os_brick/encryptors/luks.py", line 61, in __init__
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     *args, **kwargs)
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/os_brick/encryptors/cryptsetup.py", line 54, in __init__
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server     volume_type=connection_info['driver_volume_type'])
Apr 03 11:25:13 localhost.localdomain nova-compute[94660]: ERROR oslo_messaging.rpc.server VolumeEncryptionNotSupported: Volume encryption is not supported for rbd volume ba7486b3-4ea5-4715-89f3-1ec86b0d9812.