Unable to find any unassigned shards

Hi,
I am getting below error while accessing the cluster allocation through dev console with below command

GET _cluster/allocation/explain?pretty

I tried many forum solutions but still i am getting the same. Elk version is 7.2

{
  "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
}

What is the state of your cluster? How large is it?

My cluster is having 3 data nodes and 3 master nodes.

ip           heap.percent ram.percent cpu load_1m load_5m load_15m node.role master name
xxx.xx.xx.x            55          62   0    0.00    0.01     0.05 mi        *      xxxxxxxxxxx
xxx.xx.xx.x            64          98   1    0.03    0.07     0.05 di        -      xxxxxxxxxxx
xxx.xx.xx.x            63          96   4    0.20    0.27     0.22 di        -      xxxxxxxxxxx
xxx.xx.xx.x            21          43   0    0.00    0.01     0.05 mi        -      xxxxxxxxxxx
xxx.xx.xx.x            34          42   0    0.00    0.01     0.05 mi        -      xxxxxxxxxxx
xxx.xx.xx.x            58          80   4    0.13    0.30     0.21 di        -      xxxxxxxxxxx

The cluster state is green.

{
  "cluster_name" : "elkstack",
  "status" : "green",
  "timed_out" : false,
  "number_of_nodes" : 6,
  "number_of_data_nodes" : 3,
  "active_primary_shards" : 59,
  "active_shards" : 118,
  "relocating_shards" : 0,
  "initializing_shards" : 0,
  "unassigned_shards" : 0,
  "delayed_unassigned_shards" : 0,
  "number_of_pending_tasks" : 0,
  "number_of_in_flight_fetch" : 0,
  "task_max_waiting_in_queue_millis" : 0,
  "active_shards_percent_as_number" : 100.0
}

All your shards are allocated so all is well.

thanks much, but why GET _cluster/allocation/explain?pretty is giving error ? any idea ?

It says it can not find any problem shards to explain, which is a good position to be in.

ok thanks