During reproduction I saw that following trace:

Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server [None req-d3fc1ed4-04fb-4072-8df2-9e014db3714c admin admin] Exception during message handling: ResizeError: Resize error: Unable to resize disk down.
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server Traceback (most recent call last):
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/server.py", line 163, in _process_incoming
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     res = self.dispatcher.dispatch(message)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 220, in dispatch
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     return self._do_dispatch(endpoint, method, ctxt, args)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 190, in _do_dispatch
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     result = func(ctxt, **new_args)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/exception_wrapper.py", line 76, in wrapped
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     function_name, call_dict, binary)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     self.force_reraise()
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     six.reraise(self.type_, self.value, self.tb)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/exception_wrapper.py", line 67, in wrapped
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     return f(self, context, *args, **kw)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 186, in decorated_function
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     "Error: %s", e, instance=instance)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     self.force_reraise()
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     six.reraise(self.type_, self.value, self.tb)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 156, in decorated_function
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     return function(self, context, *args, **kwargs)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/utils.py", line 976, in decorated_function
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     return function(self, context, *args, **kwargs)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 214, in decorated_function
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     kwargs['instance'], e, sys.exc_info())
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     self.force_reraise()
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     six.reraise(self.type_, self.value, self.tb)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 202, in decorated_function
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     return function(self, context, *args, **kwargs)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 4272, in resize_instance
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     migration, image, disk_info, migration.dest_compute)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/contextlib.py", line 35, in __exit__
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     self.gen.throw(type, value, traceback)
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server   File "/opt/stack/nova/nova/compute/manager.py", line 7468, in _error_out_instance_on_exception
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server     raise error.inner_exception
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server ResizeError: Resize error: Unable to resize disk down.
Feb 11 00:38:53 ubuntu nova-compute[28931]: ERROR oslo_messaging.rpc.server