You may have heard of the guy that had a big beer party, and locked all of the bathroom doors.
Your site has locked out multiple attempts( about 6hrs of attempting) to download the video archives. Several times I achieved over 90 percent of the download(s) but since your site doesn’t permit Resume download, can’t get a complete download via my wireless connection.
So the issue is the timelimit on the credentials rather than a problem with restarting a download.
You should take that up with SitePoint staff and get them to extend the timelimit on the credentials so that it is valid for long enough for the dowwnload to run.