Recently, I've noticed this behavior, too. In my case it's Opera's VPN. Again. And again... I don't even remember how many times this damn VPN was a source of different problems with Opera. In recent stable 64-bit builds, if I turn the VPN on, I can't download complete files from many file-sharing services (e.g. uploaded.to, rapidgator and lots of others), Opera just downloads some megabytes and drops the connection. If I turn the VPN off, it instantly fixes the problem.

So, if you use the built-in VPN, try to turn it off and redownload your file.