We're sorry for the delay. Do you have lots of (image/video) assets on a single page; say more than a few hundred? If so, you might need to split the video into multiple pages (e.g., duplicate the page, trim the timeline to the first half on the first page, to the second half on the second page), download the pages individually, then merge them togther using the merge video quick action.
Have you tried using the other suggested browsers (Safari, Microsoft Edge, and Google Chrome) to see if it makes a difference? Try clearing the browser's cache and cookies and let us know if that helps.
I'm having a similar issue, but I think it has something to do with our companies firewall/VPN (although I'm working from campus and don't connect to a VPN from here).