Can't set up alarms

[zatmonkey]

Describe the bug
I am trying to set up alarms based on processes measurements, but it won't work - here's the trace I've got

{
  "firing": true,
  "state": "",
  "conditionEvals": " = true",
  "timeMs": "12.534ms",
  "error": "tsdb.HandleRequest() error rpc error: code = Internal desc = grpc: error while marshaling: proto: repeated field Results has nil element",
  "logs": [
    {
      "message": "Condition[0]: Query",
      "data": {
        "from": 1583346124675,
        "queries": [
          {
            "refId": "A",
            "model": {
              "alias": "node2",
              "clusterId": "XXXXXXXXX",
              "clusterName": "XXXXXXXXX",
              "database": "",
              "dimensionId": "PROCESS_CPU_USER",
              "dimensionName": "Process cpu user",
              "disk": "",
              "metricId": "process_measurements",
              "metricName": "Process Measurements",
              "mongo": "XXXXXXXXX",
              "projectId": "5b4d2c3d970199189e096df5",
              "projectName": "XXXXXXX",
              "refId": "A"
            },
            "datasource": {
              "id": 2,
              "name": "MongoDB Atlas Logs"
            },
            "maxDataPoints": 0,
            "intervalMs": 0
          }
        ],
        "to": 1583346424675
      }
    }
  ]
}

Any clue about what's going wrong?
Alerts on the system are working with all the other datasources

thanks!