Search occasionally return empty hits

[khangnguyen (Nguyen Nam Khang)]

I am observing a non-consistent behavior of ElasticSearch where the same query that yields data would occasionally return empty

{u'hits': {u'hits': [], u'total': 22724, u'max_score': 0.0}, u'_shards': {u'successful': 5, u'failed': 0, u'total': 5}, u'took': 1445, u'timed_out': False}
{u'hits': {u'hits': [], u'total': 0, u'max_score': 0.0}, u'_shards': {u'successful': 5, u'failed': 0, u'total': 5}, u'took': 388, u'timed_out': False

I am using v5.3 and Bulk Index to pour data into ElasticSearch.

Below is the query

 {
  "query": {
    "bool": {
      "must": [
        {
          "has_child": {
            "type": "ParcelOrganization",
            "filter": {
              "bool": {
                "must": [
                  {
                    "range": {
                      "imported_date": {
                        "gte": "now-14d/d"
                      }
                    }
                  }
                ]
              }
            }
          }
        },
        {
          "bool": {
            "must_not": [
              {
                "terms": {
                  "status": [
                    "delivered",
                    "pending",
                    "not_found"
                  ]
                }
              },
              {
                "exists": {
                  "field": "tt_first_attempt_business"
                }
              }
            ]
          }
        }
      ]
    }
  },
  "size": 0
}