Variable shows "None" for ES datasource

Hello

Query type variable always shows “None” and is not usable.

Grafana: 7.0.6
Elasticsearch: 7.8.0
OS: Centos 7
Browser: chrome 83

ES Index mapping:

{
  "test-idx" : {
    "mappings" : {
      "dynamic" : "strict",
      "properties" : {
        "@timestamp" : {
          "type" : "date"
        },
        "id" : {
          "type" : "keyword"
        },
        "node" : {
          "type" : "keyword"
        }
      }
    }
  }
}

Sample ES docs

{
  "@timestamp": 1594952848,
  "id": "1",
  "node": "aaa"
}

{
  "@timestamp": 1594952948,
  "id": "2",
  "node": "bbb"
}

Grafana dashboard variable
Name: node
Type: Query
Query: {“find”: “terms”, “field”: “node”}

Preview of Values: None. What could be the problem?

terms aggregation from ES works without any issue:

GET test-idx/_search
{
  "size": 0,
  "aggs": {
    "by_node": {
      "terms": {
        "field": "node"
      }
    }
  }
}

Result

  "aggregations" : {
    "by_node" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "aaa",
          "doc_count" : 1
        },
        {
          "key" : "bbb",
          "doc_count" : 1
        }
      ]
    }
  }

stupid mistake: timestamp mismatch