Count of Elastic Search index varying when querying through Presto

We are using Elassandra (Elastic Search and Cassandra) and querying on Elastic search index using presto. When we get count of index using _count API then it comes correct each time, but when we query on index to find out count using presto then it varies as shown below :

select count(*) from elasticsearch.my_schema.idx

Index mapping is shown as below :

{
  "idx": {
    "mappings": {
      "my_table": {
        "properties": {
          "col1": {
            "type": "keyword",
            "cql_collection": "singleton",
            "cql_partition_key": true,
            "cql_primary_key_order": 0
          },
          "col2": {
            "type": "keyword",
            "cql_collection": "singleton"
          }
        }
      }
    }
  }
}

Presto configuration : 1) elasticsearch.properties

connector.name=elasticsearch
elasticsearch.table-description-directory=etc/elasticsearch/
elasticsearch.scroll-size=1000
elasticsearch.scroll-timeout=30s
#elasticsearch.request-timeout=2s
elasticsearch.max-request-retries=10
elasticsearch.max-request-retry-time=90s
elasticsearch.max-hits=200000000

2) etc/elasticsearch/table.json

{
  "tableName": "my_table",
  "schemaName": "my_schema",
  "host": "10.XXX.XXX.XXX",
  "port": "9300",
  "clusterName": "my cluster",
  "index": "idx",
  "type": "my_table",
  "columns": [
      {
          "name": "col1",
          "type": "varchar",
          "jsonPath": "col1",
          "jsonType": "keyword"
      },
      {
          "name": "col2",
          "type": "varchar",
          "jsonPath": "col2",
          "jsonType": "keyword"
      }
  ]
}

We are have 3 node elassandra cluster (3 node elastic search cluster). Shards 3 and Replication 1 for this particular index. Versions :

Persto - 0.218
Elassandra - 6.2.3.21
Kibana - 6.2.3

Kindly help.