Odd/weird value of 'sort' field in sorted hits

Good afternoon. I have a problem with sorting: When I obtain the hits, they aren't sorted correctly, and every hit has a 'sort' field that normally would have as value, the value of the field im sorting with, but its not the case. I will show my mapping and query and a sample of my results.Please let me know if you need any other information.

MAPPING:

 {
  "index_name" : {
    "mappings" : {
      "typeA" : {
        "dynamic" : "strict",
        "properties" : {
          "id_offer" : {
            "type" : "long"
          },
          "id_product" : {
            "type" : "long"
          },
          "id_view_product_price" : {
            "type" : "long"
          },
          "offer_price" : {
            "type" : "double"
          },
          "price" : {
            "type" : "double"
          }
        }
      }
    }
  }
}

QUERY:

curl -XGET 'http://127.0.0.1:9200/index_name/typeA/_search?pretty' -d '
{
    "query":{
        "filtered":{
            "query":{
                "match_all":[

                ]
            },
            "filter":{
                "exists":{
                    "field":"offer_price"
                }
            }
        }
    },
    "sort":[
        {
            "offer_price":"desc"
        }
    ],
    "size":20
}'

QUERY RESPONSE:

{
  "took" : 35,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 2552,
    "max_score" : null,
    "hits" : [ {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "31046",
      "_score" : null,
      "_source":{"id_view_product_price":"31046","id_product":"7206","id_offer":"14","price":"5999.0000","offer_price":5999},
      "sort" : [ "P\u0003\u00017" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "30029",
      "_score" : null,
      "_source":{"id_view_product_price":"30029","id_product":"8375","id_offer":"6","price":"9999.0000","offer_price":5000},
      "sort" : [ "P\u0003\u00013" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27643",
      "_score" : null,
      "_source":{"id_view_product_price":"27643","id_product":"6691","id_offer":"14","price":"4999.0000","offer_price":4999},
      "sort" : [ "P\u0003\u00013" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "31048",
      "_score" : null,
      "_source":{"id_view_product_price":"31048","id_product":"6900","id_offer":"14","price":"4099.0000","offer_price":4099},
      "sort" : [ "P\u0003\u00010" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27629",
      "_score" : null,
      "_source":{"id_view_product_price":"27629","id_product":"6637","id_offer":"14","price":"4099.0000","offer_price":4099},
      "sort" : [ "P\u0003\u00010" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27590",
      "_score" : null,
      "_source":{"id_view_product_price":"27590","id_product":"6555","id_offer":"14","price":"3999.0000","offer_price":3999},
      "sort" : [ "P\u0003\u0001/" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "33605",
      "_score" : null,
      "_source":{"id_view_product_price":"33605","id_product":"8167","id_offer":"52","price":"4499.0000","offer_price":3600},
      "sort" : [ "P\u0003\u0001," ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "31047",
      "_score" : null,
      "_source":{"id_view_product_price":"31047","id_product":"6899","id_offer":"14","price":"3499.0000","offer_price":3499},
      "sort" : [ "P\u0003\u0001+" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "30449",
      "_score" : null,
      "_source":{"id_view_product_price":"30449","id_product":"5535","id_offer":"15","price":"2990.0000","offer_price":2990},
      "sort" : [ "P\u0003\u0001'" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27264",
      "_score" : null,
      "_source":{"id_view_product_price":"27264","id_product":"5533","id_offer":"14","price":"2990.0000","offer_price":2990},
      "sort" : [ "P\u0003\u0001'" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27373",
      "_score" : null,
      "_source":{"id_view_product_price":"27373","id_product":"5948","id_offer":"14","price":"2999.0000","offer_price":2999},
      "sort" : [ "P\u0003\u0001'" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "29161",
      "_score" : null,
      "_source":{"id_view_product_price":"29161","id_product":"4117","id_offer":"14","price":"2409.0000","offer_price":2409},
      "sort" : [ "P\u0003\u0001\"" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "30532",
      "_score" : null,
      "_source":{"id_view_product_price":"30532","id_product":"5697","id_offer":"15","price":"2299.0000","offer_price":2299},
      "sort" : [ "P\u0003\u0001!" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27147",
      "_score" : null,
      "_source":{"id_view_product_price":"27147","id_product":"4909","id_offer":"14","price":"2299.0000","offer_price":2299},
      "sort" : [ "P\u0003\u0001!" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27128",
      "_score" : null,
      "_source":{"id_view_product_price":"27128","id_product":"4778","id_offer":"14","price":"2219.0000","offer_price":2219},
      "sort" : [ "P\u0003\u0001!" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27123",
      "_score" : null,
      "_source":{"id_view_product_price":"27123","id_product":"4746","id_offer":"14","price":"2199.0000","offer_price":2199},
      "sort" : [ "P\u0003\u0001!" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "28918",
      "_score" : null,
      "_source":{"id_view_product_price":"28918","id_product":"3790","id_offer":"14","price":"2259.0000","offer_price":2259},
      "sort" : [ "P\u0003\u0001!" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27181",
      "_score" : null,
      "_source":{"id_view_product_price":"27181","id_product":"5115","id_offer":"14","price":"2219.0000","offer_price":2219},
      "sort" : [ "P\u0003\u0001!" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27210",
      "_score" : null,
      "_source":{"id_view_product_price":"27210","id_product":"5272","id_offer":"14","price":"2209.0000","offer_price":2209},
      "sort" : [ "P\u0003\u0001!" ]
    }, {
      "_index" : "index_name",
      "_type" : "typeA",
      "_id" : "27666",
      "_score" : null,
      "_source":{"id_view_product_price":"27666","id_product":"6737","id_offer":"14","price":"1999.0000","offer_price":1999},
      "sort" : [ "P\u0003\u0001\u001F" ]
    } ]
  }
}

At first glance seems that everything sorted correctly, but watch closely at the hits with _id "28918" and "27123", and also please notice the weird value of the "sort" field of every hit. What is wrong here? I will appreciate any help. Thanks in advance.