Not getting exact number of documents after reindexing the index

I am reindexing some indices.After the completion of reindex process,i saw that destination index has not the exact number of documents as compared to source index.

POST _reindex?max_docs=1614914&wait_for_completion=false&slices=5
{
   "source": {
    "index": "log-wlb-sysmon-2021.10.06-000001",
    "size": 5000
    
  }
  , "dest": {
    "index": "log-wlb-sysmon-2021.10.07-000003"
    
  }
}

I also reduced the size but nothing happened

health status index                            uuid                   pri rep docs.count docs.deleted store.size pri.store.size
green  open   log-wlb-sysmon-2021.10.07-000003 B-adM5RSTFaU0TumsTjofg   1   0    1614205            0      1.2gb          1.2gb
green  open   log-wlb-sysmon-2021.10.07-000002 S9IEIIiYQI-B5Yd8F7EwXg   1   1     551619        23829      725mb        359.5mb
green  open   log-wlb-sysmon-2021.10.06-000001 p1KhVH__QD6OgTXcbZQPJg   1   1    1614914        19361      1.9gb        991.2mb

I solved this problem by increasing indices.lifecycle.poll_interval value.