[Uptime] Step count sometimes incorrect

[andrewvc]

I've noticed that sometimes the step count is incorrect in the performance breakdown, showing 445 steps where there should only be 2:

I believe the root cause is that it is for some reason adding stderr events to the count, when it should just be counting the number of documents with a synthetics.type of step. See the query output below that shows this to be the case:

GET heartbeat*/_search
{
  "query": {
    "match": {
      "monitor.check_group": "a86d9b42-616f-11eb-9185-42010a84000f"
    }
  },
  "size": 0,
  "aggs": {
    "stepidx": {
      "terms": {
        "field": "synthetics.step.index"
      }
    },
    "type": {
      "terms": {
        "field": "synthetics.type"
      }
    }
  }
}


// output
{
  "took" : 32,
  "timed_out" : false,
  "_shards" : {
    "total" : 2,
    "successful" : 2,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 605,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "stepidx" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : 1,
          "doc_count" : 152
        },
        {
          "key" : 2,
          "doc_count" : 6
        }
      ]
    },
    "type" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "stderr",
          "doc_count" : 443
        },
        {
          "key" : "journey/network_info",
          "doc_count" : 145
        },
        {
          "key" : "journey/browserconsole",
          "doc_count" : 9
        },
        {
          "key" : "step/end",
          "doc_count" : 2
        },
        {
          "key" : "step/screenshot",
          "doc_count" : 2
        },
        {
          "key" : "heartbeat/summary",
          "doc_count" : 1
        },
        {
          "key" : "journey/end",
          "doc_count" : 1
        },
        {
          "key" : "journey/start",
          "doc_count" : 1
        }
      ]
    }
  }
}

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)