DataStream _bulk with duplicate _id: Unknown JSON property 'not_enabled' for type 'ResponseItem'

[MindaugasButkus]

Elastic.Clients.Elasticsearch version: 9.1.6

Elasticsearch version: 9.1.3

.NET runtime version: 8

Operating system version: Windows 11

Description of the problem including expected versus actual behavior:
Deserializer fails when it encounters a json property that it does not know how to interpret it.
This is a regression. It used to work with Elasticsearch version 9.0.2 and client version 9.0.6.

Steps to reproduce:

1. Create a data stream without enabling failure_store
2. In a single bulk operation create 2 documents with the same _id
3. Observe UnexpectedTransportException with message Unknown JSON property 'not_enabled' for type 'ResponseItem'

I executed the same steps via kibana to see what the response json payload was.
Request:

POST /mb_test/_bulk
{ "create": { "_index": "mb_test", "_id": "1" }}{ "field1": "value1", "@timestamp": "2025-09-09T15:11:10.123" }{ "create": { "_index": "mb_test", "_id": "1" }}{ "field1": "value2", "@timestamp": "2025-09-09T15:11:10.123" }

Response:

{
  "errors": true,
  "took": 0,
  "items": [
    {
      "create": {
        "_index": ".ds-mb_test-2025.09.09-000001",
        "_id": "1",
        "_version": 1,
        "result": "created",
        "_shards": {
          "total": 2,
          "successful": 1,
          "failed": 0
        },
        "_seq_no": 0,
        "_primary_term": 1,
        "status": 201
      }
    },
    {
      "create": {
        "_index": ".ds-mb_test-2025.09.09-000001",
        "_id": "1",
        "status": 409,
        "failure_store": "not_enabled",
        "error": {
          "type": "version_conflict_engine_exception",
          "reason": "[1]: version conflict, document already exists (current version [1])",
          "index_uuid": "XPy8YljrTXmkF2lZoZlBSg",
          "shard": "0",
          "index": ".ds-mb_test-2025.09.09-000001"
        }
      }
    }
  ]
}

It looks like it's failing to parse the failure_store property of the second operation.

Expected behavior
A BulkResponse with details about conflict should be returned.

Provide ConnectionSettings (if relevant):
Client created as follows:

new ElasticsearchClient(
    new ElasticsearchClientSettings(options.Uri)
        .Authentication(new ApiKey(options.ApiKey))
)

Provide DebugInformation (if relevant):

# FailureReason: Unrecoverable/Unexpected BadRequest while attempting POST on https://<node>.eastus.azure.elastic-cloud.com/<ds_name>/_bulk
 - [1] BadRequest: Node: https://<node>.eastus.azure.elastic-cloud.com/ Exception: JsonException Took: 00:00:00.1656448
# Audit exception in step 1 BadRequest:
System.Text.Json.JsonException: Unknown JSON property 'not_enabled' for type 'ResponseItem'.
   at Elastic.Clients.Elasticsearch.Core.Bulk.Json.BulkResponseItemConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Types/Core/Bulk/BulkResponseItemConverter.cs:line 114
   at Elastic.Clients.Elasticsearch.Serialization.JsonReaderExtensions.<>c__11`1.<ReadCollectionValue>b__11_0(Utf8JsonReader& r, JsonSerializerOptions o) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonReaderExtensions.cs:line 326
   at Elastic.Clients.Elasticsearch.Serialization.JsonReaderExtensions.ReadCollectionValue[T](Utf8JsonReader& reader, JsonSerializerOptions options, JsonReadFunc`1 readElement) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonReaderExtensions.cs:line 332
   at Elastic.Clients.Elasticsearch.Json.BulkResponseConverter.<>c.<Read>b__4_1(Utf8JsonReader& r, JsonSerializerOptions o) in /_/src/Elastic.Clients.Elasticsearch/_Generated/Api/BulkResponse.Converters.g.cs:line 52
   at Elastic.Clients.Elasticsearch.Json.BulkResponseConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) in /_/src/Elastic.Clients.Elasticsearch/_Generated/Api/BulkResponse.Converters.g.cs:line 52
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.ContinueDeserialize(ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack, T& value)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.DeserializeAsync(Stream utf8Json, CancellationToken cancellationToken)
   at Elastic.Transport.Products.Elasticsearch.ElasticsearchResponseBuilder.SetBodyCoreAsync[TResponse](Boolean isAsync, ApiCallDetails details, BoundConfiguration boundConfiguration, Stream responseStream, CancellationToken cancellationToken)
   at Elastic.Transport.DefaultResponseFactory.CreateCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, Exception ex, Nullable`1 statusCode, Dictionary`2 headers, Stream responseStream, String contentType, Int64 contentLength, IReadOnlyDictionary`2 threadPoolStats, IReadOnlyDictionary`2 tcpStats, CancellationToken cancellationToken)
   at Elastic.Transport.HttpRequestInvoker.RequestCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, CancellationToken cancellationToken)
   at Elastic.Transport.RequestPipeline.CallProductEndpointCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, Auditor auditor, CancellationToken cancellationToken)
   at Elastic.Transport.DistributedTransport`1.RequestCoreAsync[TResponse](Boolean isAsync, EndpointPath path, PostData data, Action`1 configureActivity, IRequestConfiguration localConfiguration, CancellationToken cancellationToken)
# Inner Exception: Unknown JSON property 'not_enabled' for type 'ResponseItem'.
System.Text.Json.JsonException: Unknown JSON property 'not_enabled' for type 'ResponseItem'.
   at Elastic.Clients.Elasticsearch.Core.Bulk.Json.BulkResponseItemConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Types/Core/Bulk/BulkResponseItemConverter.cs:line 114
   at Elastic.Clients.Elasticsearch.Serialization.JsonReaderExtensions.<>c__11`1.<ReadCollectionValue>b__11_0(Utf8JsonReader& r, JsonSerializerOptions o) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonReaderExtensions.cs:line 326
   at Elastic.Clients.Elasticsearch.Serialization.JsonReaderExtensions.ReadCollectionValue[T](Utf8JsonReader& reader, JsonSerializerOptions options, JsonReadFunc`1 readElement) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonReaderExtensions.cs:line 332
   at Elastic.Clients.Elasticsearch.Json.BulkResponseConverter.<>c.<Read>b__4_1(Utf8JsonReader& r, JsonSerializerOptions o) in /_/src/Elastic.Clients.Elasticsearch/_Generated/Api/BulkResponse.Converters.g.cs:line 52
   at Elastic.Clients.Elasticsearch.Json.BulkResponseConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) in /_/src/Elastic.Clients.Elasticsearch/_Generated/Api/BulkResponse.Converters.g.cs:line 52
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.ContinueDeserialize(ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack, T& value)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.DeserializeAsync(Stream utf8Json, CancellationToken cancellationToken)
   at Elastic.Transport.Products.Elasticsearch.ElasticsearchResponseBuilder.SetBodyCoreAsync[TResponse](Boolean isAsync, ApiCallDetails details, BoundConfiguration boundConfiguration, Stream responseStream, CancellationToken cancellationToken)
   at Elastic.Transport.DefaultResponseFactory.CreateCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, Exception ex, Nullable`1 statusCode, Dictionary`2 headers, Stream responseStream, String contentType, Int64 contentLength, IReadOnlyDictionary`2 threadPoolStats, IReadOnlyDictionary`2 tcpStats, CancellationToken cancellationToken)
   at Elastic.Transport.HttpRequestInvoker.RequestCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, CancellationToken cancellationToken)
   at Elastic.Transport.RequestPipeline.CallProductEndpointCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, Auditor auditor, CancellationToken cancellationToken)
   at Elastic.Transport.DistributedTransport`1.RequestCoreAsync[TResponse](Boolean isAsync, EndpointPath path, PostData data, Action`1 configureActivity, IRequestConfiguration localConfiguration, CancellationToken cancellationToken)
# Exception:
Elastic.Transport.UnexpectedTransportException: Unknown JSON property 'not_enabled' for type 'ResponseItem'.
 ---> System.Text.Json.JsonException: Unknown JSON property 'not_enabled' for type 'ResponseItem'.
   at Elastic.Clients.Elasticsearch.Core.Bulk.Json.BulkResponseItemConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Types/Core/Bulk/BulkResponseItemConverter.cs:line 114
   at Elastic.Clients.Elasticsearch.Serialization.JsonReaderExtensions.<>c__11`1.<ReadCollectionValue>b__11_0(Utf8JsonReader& r, JsonSerializerOptions o) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonReaderExtensions.cs:line 326
   at Elastic.Clients.Elasticsearch.Serialization.JsonReaderExtensions.ReadCollectionValue[T](Utf8JsonReader& reader, JsonSerializerOptions options, JsonReadFunc`1 readElement) in /_/src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonReaderExtensions.cs:line 332
   at Elastic.Clients.Elasticsearch.Json.BulkResponseConverter.<>c.<Read>b__4_1(Utf8JsonReader& r, JsonSerializerOptions o) in /_/src/Elastic.Clients.Elasticsearch/_Generated/Api/BulkResponse.Converters.g.cs:line 52
   at Elastic.Clients.Elasticsearch.Json.BulkResponseConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) in /_/src/Elastic.Clients.Elasticsearch/_Generated/Api/BulkResponse.Converters.g.cs:line 52
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.ContinueDeserialize(ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack, T& value)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.DeserializeAsync(Stream utf8Json, CancellationToken cancellationToken)
   at Elastic.Transport.Products.Elasticsearch.ElasticsearchResponseBuilder.SetBodyCoreAsync[TResponse](Boolean isAsync, ApiCallDetails details, BoundConfiguration boundConfiguration, Stream responseStream, CancellationToken cancellationToken)
   at Elastic.Transport.DefaultResponseFactory.CreateCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, Exception ex, Nullable`1 statusCode, Dictionary`2 headers, Stream responseStream, String contentType, Int64 contentLength, IReadOnlyDictionary`2 threadPoolStats, IReadOnlyDictionary`2 tcpStats, CancellationToken cancellationToken)
   at Elastic.Transport.HttpRequestInvoker.RequestCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, CancellationToken cancellationToken)
   at Elastic.Transport.RequestPipeline.CallProductEndpointCoreAsync[TResponse](Boolean isAsync, Endpoint endpoint, BoundConfiguration boundConfiguration, PostData postData, Auditor auditor, CancellationToken cancellationToken)
   at Elastic.Transport.DistributedTransport`1.RequestCoreAsync[TResponse](Boolean isAsync, EndpointPath path, PostData data, Action`1 configureActivity, IRequestConfiguration localConfiguration, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at Elastic.Transport.DistributedTransport`1.ThrowUnexpectedTransportException[TResponse](Exception killerException, List`1 seenExceptions, Endpoint endpoint, TResponse response, IReadOnlyCollection`1 auditTrail)
   at Elastic.Transport.DistributedTransport`1.RequestCoreAsync[TResponse](Boolean isAsync, EndpointPath path, PostData data, Action`1 configureActivity, IRequestConfiguration localConfiguration, CancellationToken cancellationToken)

I tried setting the UnmappedMemberHandling to Skip but it did not help. continue is missing here: https://github.com/elastic/elasticsearch-net/blob/main/src/Elastic.Clients.Elasticsearch/_Shared/Types/Core/Bulk/BulkResponseItemConverter.cs#L111