Unable to upload large backup files (i.e. over 1 GB) via the CLI or the GUI interface, despite the fact that smaller files are successful.
If it has been determined that this is not a networking issue, then it is potentially due to a lack of available memory on the system from which the file is being uploaded.
Try uploading the backup file from a workstation or server that has additional RAM.
Ideally, it should have more RAM free, than the size of the file in question.