Bug? "Failed to create query" error against Elasticsearch 7.3

Hi, I’m using Grafana Cloud (currently running 6.3.4, commit a557646), and am having difficulty writing queries against our Elasticsearch 7.3 deployment on Elastic cloud. The data source is configured correctly: the “Save and test” button gives me a green tick. However, when I try to query the data source from a Grafana widget, including in the Explore view, I receive an error saying “Failed to create query”. This seems to be the case for any query I write against the data source in Grafana: all the Elastic-backed widgets are blank right now. An example failed query from the error report is:

  "bool": {
    "filter": [
        "range": {
          "@timestamp": {
            "from": "1569239907225",
            "to": "1569326307225",
            "include_lower": true,
            "include_upper": true,
            "format": "epoch_millis",
            "boost": 1.0
        "query_string": {
          "query": "fields.Event.Id:19002",
          "fields": [],
          "type": "best_fields",
          "default_operator": "or",
          "max_determinized_states": 10000,
          "enable_position_increments": true,
          "fuzziness": "AUTO",
          "fuzzy_prefix_length": 0,
          "fuzzy_max_expansions": 50,
          "phrase_slop": 0,
          "analyze_wildcard": true,
          "escape": false,
          "auto_generate_synonyms_phrase_query": true,
          "fuzzy_transpositions": true,
          "boost": 1.0
    "adjust_pure_negative": true,
    "boost": 1.0

I think this is a bug, but want to rule out misconfiguration or similar first. Any ideas?