Hi, 

Just ran into this, not sure how often it happens, but sometimes size value is zero when at least I don't think it should be:

➜  curl https://api.gbif.org/v1/occurrence/download/0000739-171109162308116 | jq .
{
  "key": "0000739-171109162308116",
  "doi": "doi:10.15468/dl.jmachn",
  "license": "http://creativecommons.org/licenses/by/4.0/legalcode",
  "request": {
    "predicate": {
      "type": "greaterThanOrEquals",
      "key": "ELEVATION",
      "value": "11000"
    },
    "format": "DWCA",
    "sendNotification": false
  },
  "created": "2017-11-10T18:37:35.542+0000",
  "modified": "2017-11-10T18:38:54.444+0000",
  "status": "SUCCEEDED",
  "downloadLink": "http://api.gbif.org/v1/occurrence/download/request/0000739-171109162308116.zip",
  "size": 0,
  "totalRecords": 14064,
  "numberDatasets": 105
}

The file ends up having data in it, so it's not size 0. 

Best, 
Scott Chamberlain