Bool query with must on query_string (with date) and range does not work

[thernstig (Tobias)]

I am using Kibana to explore my Elasticsearch indices. One index stores timestamp in a "log_timestamp" field. In Kibana I've added an index pattern for this and also indicated that the "log_timestamp" field is the one to look for for Dates. I select a time range in the time picker from todays date and two years back. I also add a Lucene query on the timestamp. The HTTP body sent by Kibana looks like this.

{
  "version": true,
  "size": 500,
  "sort": [
    { "log_timestamp": { "order": "desc", "unmapped_type": "boolean" } }
  ],
  "_source": { "excludes": [] },
  "aggs": {
    "2": {
      "date_histogram": {
        "field": "log_timestamp",
        "calendar_interval": "1w",
        "time_zone": "Europe/Stockholm",
        "min_doc_count": 1
      }
    }
  },
  "stored_fields": ["*"],
  "script_fields": {},
  "docvalue_fields": [
    { "field": "@timestamp", "format": "date_time" },
    { "field": "log_timestamp", "format": "date_time" }
  ],
  "query": {
    "bool": {
      "must": [
        {
          "query_string": {
            "query": "log_timestamp:[2019-05-20 TO 2019-10-20]",
            "analyze_wildcard": true,
            "time_zone": "Europe/Stockholm"
          }
        },
        {
          "range": {
            "log_timestamp": {
              "format": "strict_date_optional_time",
              "gte": "2017-10-03T07:18:10.889Z",
              "lte": "2019-10-03T07:18:10.889Z"
            }
          }
        }
      ],
      "filter": [],
      "should": [],
      "must_not": []
    }
  },
  "highlight": {
    "pre_tags": ["@kibana-highlighted-field@"],
    "post_tags": ["@/kibana-highlighted-field@"],
    "fields": { "*": {} },
    "fragment_size": 2147483647
  },
  "timeout": "30000ms"
}

The problem I am having is that this returns a "No results match your search criteria". There should have been documents that match both of these MUST parts. I must misunderstand the bool query somehow. If I change my query to: log_timestamp:*
then it works fine and I get plenty of results.

What am I missing?