I am getting these errors. Data is loaded into elasticsearch, but some records are missing in kibana. I am seeing this in fluentd logs in kubernetes

2021-04-26 15:58:10 +0000 [warn]: #0 failed to flush the buffer. retry_time=29 next_retry_seconds=2021-04-26 15:58:43 +0000 chunk="5c0e21cad29fc91298a9d881c6bd9873" error_class=Fluent::Plugin::ElasticsearchErrorHandler::ElasticsearchError error="Elasticsearch returned errors, retrying. Add '@log_level debug' to your config to see the full response"
  2021-04-26 15:58:10 +0000 [warn]: #0 suppressed same stacktrace

Here is myy fluentd conf

  fluent.conf: |
    <match fluent.**>
        # this tells fluentd to not output its log on stdout
        @type null
    </match>
    # here we read the logs from Docker's containers and parse them
    <source>
      @type tail
      path /var/log/containers/*nginx-ingress-controller*.log,/var/log/containers/*kong*.log
      pos_file /var/log/nginx-containers.log.pos
      @label @NGINX
      tag kubernetes.*
      read_from_head true
      <parse>
        @type json
        time_format %Y-%m-%dT%H:%M:%S.%NZ
      </parse>
    </source>
    <source>
      @type tail
      path /var/log/containers/*.log
      exclude_path ["/var/log/containers/*nginx-ingress-controller*.log", "/var/log/containers/*kong*.log"]
      pos_file /var/log/fluentd-containers.log.pos
      tag kubernetes.*
      read_from_head true
      <parse>
        @type json
        time_format %Y-%m-%dT%H:%M:%S.%NZ
      </parse>
    </source>
    # we use kubernetes metadata plugin to add metadatas to the log
    <filter kubernetes.**>
        @type kubernetes_metadata
    </filter>
    <label @NGINX>
        <filter kubernetes.**>
            @type kubernetes_metadata
        </filter>
        <filter kubernetes.**>
          @type parser
          key_name log
          reserve_data true
          <parse>
            @type regexp
            expression /^(?<remote>[^ ]*(?: [^ ]* [^ ]*)?) (?<host>[^ ]*) (?<user>[^ ]*) \[(?<time>[^\]]*)\] "(?<method>\S+)(?: +(?<path>[^\"]*?)(?: +\S*)?)?" (?<code>[^ ]*) (?<size>[^ ]*)(?: "(?<referer>[^\"]*)" "(?<agent>[^\"]*)"(?: (?<request_length>[^ ]*) (?<request_time>[^ ]*) (?<proxy_upstream_name>[^ ]*(?: \[[^ ]*\])*) (?<upstream_addr>[^ ]*(?:, [^ ]*)*) (?<upstream_response_length>[^ ]*(?:, [^ ]*)*) (?<upstream_response_time>[^ ]*(?:, [^ ]*)*) (?<upstream_status>[^ ]*(?:, [^ ]*)*) (?<req_id>[^ ]*))?)?$/
            time_format %d/%b/%Y:%H:%M:%S %z
          </parse>
        </filter>
        <match kubernetes.**>
            @type elasticsearch
            include_tag_key true
            host "#{ENV['FLUENT_ELASTICSEARCH_HOST']}"
            port "#{ENV['FLUENT_ELASTICSEARCH_PORT']}"
            scheme "#{ENV['FLUENT_ELASTICSEARCH_SCHEME'] || 'https'}"
            ssl_verify false
            reload_connections false
            logstash_prefix k8-nginx
            logstash_format true
            <buffer>
                 flush_mode interval
                 retry_type exponential_backoff
                 flush_thread_count 2
                 flush_interval 5s
                 retry_forever true
                 retry_max_interval 30
                 chunk_limit_size 2M
                 queue_limit_length 32
                 overflow_action block
            </buffer>
        </match>
    </label>
    # we send the logs to Elasticsearch
    <match kubernetes.**>
        @type elasticsearch
        include_tag_key true
        host "#{ENV['FLUENT_ELASTICSEARCH_HOST']}"
        port "#{ENV['FLUENT_ELASTICSEARCH_PORT']}"
        scheme "#{ENV['FLUENT_ELASTICSEARCH_SCHEME'] || 'https'}"
        ssl_verify false
        reload_connections false
        logstash_prefix k8-logstash
        logstash_format true
        <buffer>
               flush_mode interval
               retry_type exponential_backoff
               flush_thread_count 2
               flush_interval 5s
               retry_forever true
               retry_max_interval 30
               chunk_limit_size 2M
               queue_limit_length 32
               overflow_action block
        </buffer>
    </match>