>>1778I've never had this issue, but for what it's worth IA offers to download via Bittorrent on every single file.
If there's something you really like there you can even use the various decentralized swarms (or just add the most common public trackers) and seed it yourself should IA ever take the file down.
I've never used this feature since I've only downloaded 1GB files at most and I'd rather just download it and upload a normal torrent elsewhere with appropriate trackers included, but it seems like it would be good for your usecase if you're trying to download massive files.
Notably firefox supposedly does support pausing and resuming downloads though, but it's possible there's some type of authentication making it think it's a new file.
Did you open the downloads tab to press resume or did you click the download link again?