Well, that's certainly a puzzle. Do you get the same when you download https://broth.itch.ovh/install-itch/windows-386/_25/unpacked/default directly ?
Also, which country is that from? (VPN-less and VPN). What does the network look like? Is it possible anyone on your network (ISP, etc.) is trying to disrupt SSL traffic? Asking because this is the first report I'm seeing of this.