I set up a workaround on the server that should fix Legacy Update being blocked by some ISPs (specifically, I just set up a new subdomain and redirected all Windows Update download traffic through there).
If you’ve been running into “Windows Update may be blocked by your firewall or proxy server” or error 8024402F, try again now, it should work. If not, you may need to force Windows Update to grab an updated list of download links from our server by deleting the C:\Windows\SoftwareDistribution folder and trying again.