Large number of _unknown_ namespace keep AddWorkflowTask

counters.temporal.service_requests.namespace.unknown.operation.AddWorkflowTask
Seeing large number of unknown namespace keep AddWorkflowTask, even though no new workflow has been scheduled. Any idea why there is such symptom?

It could be caused by workflow tasks failing for already open workflows.

the only way to remove them is wait for workflow to timeout and these will go away I guess?

You can terminate stuck workflows.