Error: Download manager failed to download from (a user_uploads URL)

[borisyankov]

https://sentry.io/zulip/zulip-mobile/issues/501654438/

Error: Download manager failed to download from  https://machlearn.zulipchat.com/user_uploads/1129/uv_4kv70vLzFF7hLpBgEfAcN/mat8.PNG. Statu Code = 16
    at react-native-fetch-blob/index.prototype(index.js:329)
    count = args[0].count || count
    at react-native/Libraries/BatchedBridge/MessageQueue.__guard(MessageQueue.js:102)
    MessageQueue.prototype.__spy = info => {
    at react-native/Libraries/BatchedBridge/MessageQueue._inCall(MessageQueue.js:146)
    this.__guard(() => {
    at react-native/Libraries/BatchedBridge/MessageQueue.flushedQueue(MessageQueue.js:320)
    this._inCall--;
    at react-native/Libraries/BatchedBridge/MessageQueue.value(MessageQueue.js:142)
    return this.flushedQueue();

[gnprice]

This looks likely to be related to #2618 .