Self-hosted prebid Java sever issue: Processing stored requests fails: "Invalid request format: Stored request processing failed"

Question

Such a POST request fails with the error mentioned above:

POST https://prebid.ourhost.com/openrtb2/auction
Accept-Language: en_US
Accept: application/x-www-form-urlencoded,application/json,text/plain,text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-Agent: Dalvik/2.1.0 (Linux; U; Android 11; Mi 9 SE Build/RKQ1.200826.002)
Host: prebid.ourhost.com
Content-Type: application/json

{
  "site": {
    "id": "site"
  },
  "imp": [
    {
      "id": "2fe98dd5-2682-41e4-b4c7-7d72fecbd204",
      "banner": {
        "format": [
          {
            "w": 320,
            "h": 50
          }
        ]
      },
      "ext": {
      "appnexus": {
        "placementId": 12883451
      },
        "prebid": {
          "storedauctionresponse": {
            "id": "abc03e7c-bf36-40cb-a28f-ce614214ea1a"
          }
        }
      }
    }
  ],
  "test": 1,
  "id": "2fe98dd5-2682-41e4-b4c7-7d72fecbd204",
  "ext": {
    "prebid": {
      "storedrequest": {
        "id": "4e854e76-d0fd-4f33-8655-259603a9f491"
      }
    }
  }
}

If I use "ext": {} instead of

"ext": {
    "prebid": {
      "storedrequest": {
        "id": "4e854e76-d0fd-4f33-8655-259603a9f491"
      }
    }
  }

the request succeeds.

The stored request is in a MySQL database: 4e854e76-d0fd-4f33-8655-259603a9f491,{"tmax": 2000}

This is the configuration option (same as https://docs.prebid.org/prebid-server/hosting/pbs-database.html): stored-requests-query: SELECT uuid, config, 'request' as dataType FROM stored_requests WHERE uuid IN (%REQUEST_ID_LIST%) UNION ALL SELECT uuid, config, 'imp' as dataType FROM stored_imps WHERE uuid IN (%IMP_ID_LIST%)

I know that the DB connection works fine, because if I use an invalid ID, I get "No stored requests for ids" response.

I also tried using an additional account ID column, as specified in https://docs.prebid.org/prebid-server/features/pbs-storedreqs-java.html, but the documentation is probably wrong in this case, because then I get "Can't parse Json for stored request with id"

Is this a bug? Or should the stored request JSON format be different?