Working elasticsearch 5 query don't work in 6.2 (reason : all shards failed)

[Webmaster_Cerf]

Hello after an upgrade to 6.2 my ajax requests to elasticsearch fails with this message :
An uncaught Exception was encountered
Type: Elastica\Exception\ResponseException

    "bool" : {
"must" : [
  {
    "query_string" : {
      "query" : "*18S",
      "fields" : [
        "n_stage^1.0"
      ],
      "type" : "best_fields",
      "default_operator" : "or",
      "max_determinized_states" : 10000,
      "enable_position_increments" : true,
      "fuzziness" : "AUTO",
      "fuzzy_prefix_length" : 0,
      "fuzzy_max_expansions" : 50,
      "phrase_slop" : 0,
      "escape" : false,
      "auto_generate_synonyms_phrase_query" : true,
      "fuzzy_transpositions" : true,
      "boost" : 1.0
    }
  }
],
"should" : [
  {
    "query_string" : {
      "query" : "par~3",
      "fields" : [
        "contenu^1.0",
        "intitule_stage^3.0",
        "mmp^1.0",
        "mots_cles^3.0",
        "objectifs^1.0",
        "sessions.ville^5.0"
      ],
      "type" : "best_fields",
      "default_operator" : "or",
      "max_determinized_states" : 10000,
      "enable_position_increments" : true,
      "fuzziness" : "AUTO",
      "fuzzy_prefix_length" : 0,
      "fuzzy_max_expansions" : 50,
      "phrase_slop" : 0,
      "escape" : false,
      "auto_generate_synonyms_phrase_query" : true,
      "fuzzy_transpositions" : true,
      "boost" : 1.0
    }
  }
],
"adjust_pure_negative" : true,
"boost" : 1.0

}
} [index: cerf] [reason: all shards failed]

have you an idea where is the problem ? The message suggest my server could be down but it works.

Thanks for your help