The download of a backup via the StageWare Manager aborts before finishing.
If the download quits at various points of the process, it could be due to your computer or your network. Try downloading the backup using a different computer and/or network.
If the download always quits at the same point of the process, this could be caused by your server. On an nginx web server there is a setting "proxy_max_temp_file_size" which must be set to larger than the backup.