At this point please don’t use IDM. It is a fine download manager, but it has a problem with https downloads. It can’t spawn multiple connections and resume broken downloads when downloading via https. If you remove the s at the end of https it will work correctly. We couldn’t find the cause of this. It can’t download https content from Dropbox, either, so it’s not us.
A good download manager that just works everywhere is DownThemAll, a Firefox extension. You can get it from here: https://addons.mozilla.org/en-US/firefox/addon/downthemall/ It’s worth it even if you don’t use Firefox, you can think of the combo itself as a download manager. However, we've recently had several reports of more frequent timeouts with DownThemAll, which can be fixed by increasing the timeout setting to a higher number, so please keep that in mind. (Note: Currently not compatible with Firefox Quantum.)
We've also recently discovered Motrix and we think it's definitely worth giving a try. It's compatible with all three - macOS, Windows, and Linux. (And it's open source - yay!)
Mac users seem to like EasyGet and EasyGet Lite (free), on the Mac Appstore, and Progressive Downloader here. Linux users like aria2. And to PC users we’ve been recommending the Free download manager or FDM
There is also the fact that if you take a long time to download something, your ISP might change your IP in the middle of the download. In that case, your download link becomes invalid, because the token in the link is derived from your IP address.
If that happens even your download manager will not be able to resume, what you need to do is refresh the page at put.io and get a new download link, then update the link on your download manager.
Finally, here’s a good resource for comparing different download managers: https://en.wikipedia.org/wiki/Comparison_of_download_managers