Comment 5 for bug 1907686

Also see a few of these:
2021-01-12 06:48:21.947 52569 INFO eventlet.wsgi.server [-] 10.5.3.232,<local> "GET /openstack HTTP/1.1" status: 500 len: 362 time: 0.0006430
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server [-] Unexpected error.: AttributeError: 'MetadataProxyHandler' object has no attribute 'sb_idl'
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server Traceback (most recent call last):
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server File "/usr/lib/python3/dist-packages/neutron/agent/ovn/metadata/server.py", line 67, in __call__
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server instance_id, project_id = self._get_instance_and_project_id(req)
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server File "/usr/lib/python3/dist-packages/neutron/agent/ovn/metadata/server.py", line 84, in _get_instance_and_project_id
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server ports = self.sb_idl.get_network_port_bindings_by_ip(network_id,
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server AttributeError: 'MetadataProxyHandler' object has no attribute 'sb_idl'
2021-01-12 06:48:49.848 52569 ERROR neutron.agent.ovn.metadata.server

Restarting the neutron-ovn-metadata-agent service resolves the issue.