No doc was generated while rollup job stats indicate processing

[simmonHuong]

{
  "config": {
    "id": "rollup_myindex_2018_by_7d",
    "index_pattern": "myindex_2018*",
    "rollup_index": "rolledup_myindex_2018",
    "cron": "0 * * * * ?",
    "groups": {
      "date_histogram": {
        "interval": "7d",
        "field": "create_time",
        "delay": "1d",
        "time_zone": "Asia/Taipei"
      },
      "terms": {
        "fields": [
          "member_id",
          "company.keyword",
          "action"
        ]
      }
    },
    "metrics": [
      {
        "field": "amount",
        "metrics": [
          "sum"
        ]
      },
      {
        "field": "field_a",
        "metrics": [
          "sum"
        ]
      },
      {
        "field": "field_b",
        "metrics": [
          "sum"
        ]
      }
    ],
    "timeout": "20s",
    "page_size": 1000
  },
  "status": {
    "job_state": "started",
    "current_position": {
      "action.terms": "RUN",
      "company.keyword.terms": "SUN",
      "create_time.date_histogram": 1545235200000,
      "member_id.terms": 411134380
    },
    "upgraded_doc_id": true
  },
  "stats": {
    "pages_processed": 399,
    "documents_processed": 125052292,
    "rollups_indexed": 350444,
    "trigger_count": 48
  }
}

But hours later I don't see any doc generated.

health status index                         uuid                   pri rep docs.count docs.deleted store.size pri.store.size
green  open   rolledup_myindex_2018 AK3mVDWKRn2FM72dkz1P7Q   3   1          0            0      1.5kb           783b

elasticsearch: 6.5.4
kibana: 6.5.4