Unable to find any unassigned shards to explain in Elasticsearch.

Issue

• Unable to find any unassigned shards to explain in Elasticsearch.
• The es_util --query=_cluster/allocation/explain?pretty shows unable to find any unassigned shards to explain

# oc es_pod  -- es_util --query=_cluster/allocation/explain?pretty
Defaulting container name to elasticsearch.
Use 'oc describe pod/logging-es-data-master-xxxx -n openshift-logging' to see all of the containers in this pod.
{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "unable to find any unassigned shards to explain [ClusterAllocationExplainRequest[useAnyUnassignedShard=true,includeYesDecisions?=false]"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "unable to find any unassigned shards to explain [ClusterAllocationExplainRequest[useAnyUnassignedShard=true,includeYesDecisions?=false]"
  },
  "status" : 400
}