自定义评分查询，部分分片报错

版本elasticsearch6.0.0，某一个索引有5个分片，在进行如下检索时，检索某些词会出现某个分片报错的情况（不是所有词都报错，只是部分词），经检查发现报错的文档id根本没有存储在该分片上，而是在其他分片上；求大神能不能分析一下。
请求：

{

  "from": 0, 

  "size": 2, 

  "query": {

    "function_score": {

      "query": {

        "bool": {

          "must": [

            {

              "multi_match": {

                "query": "我知道", 

                "fields": [

                  "nickname^1.4",

                  "summary^1.0",

                  "title^1.3"

                ], 

                "type": "best_fields", 

                "operator": "OR", 

                "slop": 0, 

                "prefix_length": 0, 

                "max_expansions": 50, 

                "minimum_should_match": "2<75%", 

                "lenient": false, 

                "cutoff_frequency": 0.01, 

                "zero_terms_query": "NONE", 

                "boost": 1

              }

            }

          ], 

          "filter": [

            {

              "term": {

                "status": {

                  "value": 0, 

                  "boost": 1

                }

              }

            }

          ], 

          "adjust_pure_negative": true, 

          "boost": 1

        }

      }, 

      "functions": [

        {

          "filter": {

            "match_all": {

              "boost": 1

            }

          }, 

          "field_value_factor": {

            "field": "reply_count", 

            "factor": 1, 

            "missing": 1, 

            "modifier": "ln2p"

          }

        }

      ], 

      "score_mode": "sum", 

      "boost_mode": "sum", 

      "max_boost": 3.4028235e+38, 

      "boost": 1

    }

  }

}

错误信息：

{

    "took": 13,

    "timed_out": false,

    "_shards": {

        "total": 5,

        "successful": 4,

        "skipped": 0,

        "failed": 1,

        "failures": [

            {

                "shard": 1,

                "index": "post_one",

                "node": "09elmBYOQ1Sx7084BTTAQw",

                "reason": {

                    "type": "exception",

                    "reason": "function score query returned an invalid score: NaN for doc: 9117"

                }

            }

        ]

    },

    "hits": {

        "total": 20859,

        "max_score": 15.510478,

        "hits": [

            {

        ………………

}