Score is 0 when using function score on nested documents

Elastic Stack Elasticsearch
1

Hi,

Having the following mapping, 'reviews.positive.aspects' is a nested array:

{
   "template":"products*",
   "mappings":{
   "Product":{
     "dynamic":"false",
     "properties":{
        "id":{
           "type":"long"
        },
        "name":{
           "type":"string",
           "analyzer":"standard"
        },
        "score":{
           "type":"double"
        },
        "reviews":{
           "type":"nested",
           "dynamic":"false",
           "properties":{
              "positive":{
                 "type":"nested",
                 "dynamic":"false",
                 "properties":{
                    "reviewCount":{
                       "type":"integer"
                    },
                    "quote":{
                       "type":"string",
                       "analyzer":"standard"
                    },
                    "aspects":{
                       "type":"nested",
                       "dynamic":"false",
                       "properties":{
                          "id":{
                             "type":"long"
                          },
                          "name":{
                             "type":"string",
                             "analyzer":"standard"
                          },
                          "score":{
                             "type":"double"
                          },
                          "frequency":{
                             "type":"integer"
                          }
                       }
                    }
                 }
              }
           }
        }
     }
  }
   }
}

I'm trying to set a query to match documents with with score higher than X, aspects.score higher than Y and aspects.id equals to Z, and results sorted by aspects.frequency. I'm using FunctionScoreQuery, but all scores in the results are 0. Here is my code:

        AndFilterBuilder aspectFilter = andFilter( termFilter( "reviews.positive.aspects.id", aspectId ), rangeFilter( "reviews.positive.aspects.score" ).from( aspectScore ).includeLower( true ) );

	NestedFilterBuilder nestedAspectFilter = nestedFilter( "reviews.positive.aspects", filteredQuery( matchAllQuery(), aspectFilter ) );

	RangeFilterBuilder productScoreFilter = rangeFilter( "score" ).from( productScore ).includeLower( true );

	QueryBuilder productScoreQuery = filteredQuery( matchAllQuery(), andFilter( productScoreFilter ) );

	QueryBuilder aspectScoreQuery = QueryBuilders.nestedQuery( "reviews", filteredQuery( matchAllQuery(), nestedAspectFilter ) );
	
	String inlineScript = "doc['reviews.positive.aspects.frequency'].value";
	
	ScoreFunctionBuilder sfb = ScoreFunctionBuilders.scriptFunction( inlineScript, "groovy" );
	
	FunctionScoreQueryBuilder functionScore = QueryBuilders.functionScoreQuery( boolQuery().must( productScoreQuery ).must( aspectScoreQuery ), nestedAspectFilter, sfb );

            client.prepareSearch( "products" ).
                 setQuery( functionScore ).
                  addSort( SortBuilders.scoreSort().order( SortOrder.DESC) ).
                  setSearchType( SearchType.QUERY_THEN_FETCH ).
	      get();

The explain looks as follow (similar to all docs):

 0.0 = (MATCH) function score, product of:
  0.0 = (MATCH) Math.min of
    0.0 = script score function, computed with script:"doc['reviews.positive.aspects.frequency'].value
      1.4142135 = _score: 
        1.4142135 = (MATCH) sum of:
          0.70710677 = (MATCH) ConstantScore(+cache(score:[8.0 TO *]) , product of:
            1.0 = boost
            0.70710677 = queryNorm
          0.70710677 = (MATCH) Score based on child doc range from 110571 to 110598
    3.4028235E38 = maxBoost
  1.0 = queryBoost

Documents in the results indeed match the filtering criteria, but not sorted (and score is 0). Can you direct me how should I fix the code?

Thanks!