I'm having issues trying to install on a Surface Go with Windows 10 Pro, same starting error with different text below. I'm guessing they're just getting absolutely slammed with all this traffic and will probably right itself afterwards.
itch-setup, v1.18.0, built on Apr 10 2019 @ 07:28:23, ref
57838bc373361f2c8938336674247f869999e862
broth.itch.ovh: HTTP 404: Invalid file requested
etc...