No idea if this is a problem from Humble Bundle or Aseprite developer, so I post the issue here for now and will move to Humble Bundle support if needed.
I tried to download latest version of Aseprite 1.2.9 from my Humble Bundle library, but the Aseprite 64-bit for Linux link starts a download that stays at 0% with undetermined remaining time forever. All the other versions (32-bit and beta) work fine. So I’m wondering if it’s not a server issue but a bug due to a wrong file being uploaded just for that version. Could you please check the files you uploaded on Humble Bundle?
If everything seems fine on your side, I’ll report the bug to Humble Bundle (or you can if you think it’s not an isolated issue).