When downloading I sometimes hid the following error
DownloadFailedException(_create_download_failed_message(exception))
sentinelhub.download.DownloadFailedException: Failed to download with HTTPError:
503 Server Error: Service Unavailable for url:
It might be, that there is a temporary interruption on one of our servers. These kind of events are rare, but normal in cloud based environment with millions requests being processed every day.
We recommend you perform a retry when such error occurs.