It's not a "bug", the installer works by reading the version online, and the one and only version we have online now, is 3.5.7 and that's what most users see. There's no version 3.5.6 anywhere on our site.
You are seeing version 3.5.6 as the last one, because your local cloudflare node is serving you an outdated version of the site that doesn't exists anymore so yes, you should use a VPN and try other locations.