Because the file manager within the Control Panel is a web-based FTP system, it does suffer from certain limitations due to having to run in a browser, and your browser/ISP connection is likely to be timing out before upload completes.
To avoid this issue, if you need to upload large files to your website, then we'd recommend you use an FTP client to do so, such as
FileZilla
Using an FTP client would mean you are using a dedicated piece of software for the purpose of FTP file transfer, and they are much more reliable in their connections, especially regarding large files.
