I don't understand what's wrong, logstash doesn't work with grok?

Question

logstash

assembled a simple filter

filter {
  if [type] == "rsyslog"{
    grok {
      add_tag => "TEST"
    }
  }
}

Logstash in debug mode produces the following

[2018-10-21T23:12:58,284][DEBUG][logstash.pipeline        ] output received {"event"=>{"tags"=>["<b>_grokparsefailure</b>"], "facility"=>"user", "sysloghost"=>"gateway", "type"=>"rsyslog", "procid"=>"-", "severity"=>"notice", "@timestamp"=>2018-10-21T20:12:58.178Z, "programname"=>"dns,packet", "host"=>"127.0.0.1", "message"=>" question: ftp.local:A:IN", "@version"=>"1"}}

correctly I understand that with the tag "_grokparsefailure" grok does not process?
PS: the logs themselves go to the cluster.


{
  "_index": "logstash-2018.10.21",
  "_type": "doc",
  "_id": "TOtFmGYBF3439qZqD331",
  "_version": 1,
  "_score": null,
  "_source": {
    "tags": [
      "_grokparsefailure"
    ],
    "facility": "daemon",
    "sysloghost": "shtirliz",
    "type": "rsyslog",
    "procid": "-",
    "severity": "notice",
    "@timestamp": "2018-10-21T20:15:54.565Z",
    "programname": "systemd",
    "host": "127.0.0.1",
    "message": "Unit auditbeat.service entered failed state.",
    "@version": "1"
  },
  "fields": {
    "@timestamp": [
      "2018-10-21T20:15:54.565Z"
    ]
  },
  "highlight": {
    "tags": [
      "_grokparsefailure"
    ]
  },
  "sort": [
    1540152954565
  ]
}