Same problem, tried to download a couple freebies, needed a few dozen retries (on slow internet, but still).

I had similar issues with Github releases recently - according to their support it is an Amazon cloud thing (where they host their files, I think Renderosity does as well?).

The biggest annoyance is not even that the downloads stop at some point, but that you can not resume them ('blahblah FORBIDDEN'), you have to start over.

This is something browsers and download managers have been able to do since the 1990s and modern 'cloud services' saw the need to break it, probably because the developers sit on 5000 TB/s optical fiber and can not imagine there are still people out there where downloads take longer than a few nanoseconds...