input.mqtt packet loss

Relevant telegraf.conf

## Read metrics from MQTT topic(s)
[[inputs.mqtt_consumer]]
  alias = "mqtt_consumer"
  ## Broker URLs for the MQTT server or cluster.  To connect to multiple
  ## clusters or standalone servers, use a separate plugin instance.
  ##   example: servers = ["tcp://localhost:1883"]
  ##            servers = ["ssl://localhost:1883"]
  ##            servers = ["ws://localhost:1883"]
  servers = ["tcp://xxxxx:1883"]

  ## Topics that will be subscribed to.
  topics = [
    #"company/country/site/device_type/device_id/Data",
    "+/+/+/+/+/Data"
  ]

  ## The message topic will be stored in a tag specified by this value.  If set
  ## to the empty string no topic tag will be created.
  topic_tag = "topic"

  ## QoS policy for messages
  ##   0 = at most once
  ##   1 = at least once
  ##   2 = exactly once
  ##
  ## When using a QoS of 1 or 2, you should enable persistent_session to allow
  ## resuming unacknowledged messages.
  qos = 1

  ## Connection timeout for initial connection in seconds
  # connection_timeout = "30s"

  ## Maximum messages to read from the broker that have not been written by an
  ## output.  For best throughput set based on the number of metrics within
  ## each message and the size of the output's metric_batch_size.
  ##
  ## For example, if each message from the queue contains 10 metrics and the
  ## output metric_batch_size is 1000, setting this to 100 will ensure that a
  ## full batch is collected and the write is triggered immediately without
  ## waiting until the next flush_interval.
  max_undelivered_messages = 5000

  ## Persistent session disables clearing of the client session on connection.
  ## In order for this option to work you must also set client_id to identify
  ## the client.  To receive messages that arrived while the client is offline,
  ## also set the qos option to 1 or 2 and don't forget to also set the QoS when
  ## publishing.
  persistent_session = false

  ## If unset, a random client ID will be generated.
  client_id = "collector"

  ## Username and password to connect MQTT server.
  username = "xxx"
  password = "xxx"

  ## Optional TLS Config
  # tls_ca = "/etc/telegraf/certs/ca-bundle.crt"
  # tls_cert = "/etc/telegraf/certs/client.crt"
  # tls_key = "/etc/telegraf/certs/client.key"
  ## Use TLS but skip chain & host verification
  # insecure_skip_verify = false
  
  ## Client trace messages
  ## When set to true, and debug mode enabled in the agent settings, the MQTT
  ## client's messages are included in telegraf logs. These messages are very
  ## noisey, but essential for debugging issues.
  client_trace = false

  ## Data format to consume.
  ## Each data format has its own unique set of configuration options, read
  ## more about them here:
  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
  data_format = "influx"

[[inputs.internal]]
  ## If true, collect telegraf memory stats.
  collect_memstats = true
  [inputs.internal.tags]
    host = "collector"

Logs from Telegraf

No errors detected in the logs, even activating traces.

System info

Telegraf 1.34.4, RHEL 7 + Docker

Docker

No response

Steps to reproduce

1. Subscribe to several topics using wildcard. "+/+/+/+/+/Data"
2. Subscribe to one unique topic. "company/country/site/device_type/device_id/Data"
3. Compare result and verify that for several topics, even indicating QoS=1 there are packet loss.

Expected behavior

All the packets should be collected without any loss of data.

Actual behavior

Packet loss. Comparison of single vs multiple topics.

1. Variable 1 collected by a mqtt.input telegraf config with single topic subscription.
2. Variable 1 collected by a mqtt.input telegraf config with wilcard subscription.
3. Variable 2 collected by a mqtt.input telegraf config with single topic subscription.
4. Variable 2 collected by a mqtt.input telegraf config with wilcard subscription.

Additional info

No response

Start with the inputs.mqtt_consumer entry point and reproduce the comparison between the wildcard subscription "+/+/+/+/+/Data" and the single topic subscription. Use the provided Telegraf configuration and logs to investigate the reported packet loss; done means collecting the same packets without loss for both subscription patterns.