I'm not sure what the issue is, the downloads are working fine on a few different computers for us and the MEGA side of things seem to be in order. There shouldn't be any need for installing though, you should just unzip the file and it should play just fine.
When using the Itch client for updates/managing their collections, it requires you to have a specific tag for each system your game supports. When it's setup like this, users are unable to download and install or manage updates with it. That's why it won't "install" for Hugo. It doesn't really install, but it just bypasses the unzipping and future managing steps for the user as far as I know.
Thanks for the info! It seems a little odd that I would have to specifically use a separate uploading manager to have uploaded games work with the itch.io client as opposed to simply having the client download the .zip normally. As of now our game is tagged correctly with what systems the game supports, however the client still does not download the files correctly. I would suggest downloading our game not using the client at the moment, and just from a web browser.