Cannot get scrolling to work when trying to extract more than 10,000 results

[terry433iid (turlough)]

I have an index ('jenkins_job_logs') that stores console logs from jenkins jobs, the index fields include the actual console data plus a unique ID for the jenkins job ('task_id'), there are 30k plus documents in the index so I am unable to extract more than 10k at a time

(am not going to modify the value of index.max_result_window)

So will use scrolling instead - but am hitting an issue

Here is the initial query

    elk>cat testquery2.json
    {
        "_source": {
            "includes" : [ "task_id" ],
            "excludes" : [ "console_data", "testsuite", "os_name", "host_vm_version", "guest_vm_version" ]
        },
        "size": 5000,
        "query": {
           "match_all" : {}
        }
    }

When I run the query below I get 5000 matches returned, plus a scroll ID (have shortened the ID as it is 3200_ chars long)

    elk>curl -XGET 'http://localhost:9200/jenkins_job_logs-2020.*/_search?scroll=1m&pretty' -H "Content-Type: application/json" -d @testquery2.json
    {
      "_scroll_id" : "DnF1ZXJ5VGhlbk..<3622 characters long>..ZldGNoVwAAAAAA=="
      "took" : 17087,
      "timed_out" : false,
      "_shards" : {
        "total" : 87,
        "successful" : 87,
        "skipped" : 0,
        "failed" : 0
      },
      "hits" : {
        "total" : 32314,
        "max_score" : 1.0,
        "hits" : [
          {
            "_index" : "jenkins_job_logs-2020.07.28",
            "_type" : "doc",
            "_id" : "1419",
            "_score" : 1.0,
            "_source" : {
              "task_id" : 187873
            }
          },
          {
            "_index" : "jenkins_job_logs-2020.07.28",
            "_type" : "doc",
            "_id" : "273",
            "_score" : 1.0,
            "_source" : {
              "task_id" : 186542
            }

I then plug the scroll ID above into a new search command (as per the docs) and get the error below

    elk>curl -XPOST 'http://localhost:9200/_search/scroll?pretty' -H "Content-Type: application/json"  -d '{"scroll" : "1m", "scroll_id" : "DnF1ZXJ5VGhlbk..<3622 characters long>..ZldGNoVwAAAAAA=="
    {
      "error" : {
        "root_cause" : [
          {
            "type" : "search_context_missing_exception",
            "reason" : "No search context found for id [1910847]"
          },
          {
            "type" : "search_context_missing_exception",
            "reason" : "No search context found for id [1910856]"
          },