Hoogle 4, the old version at haskell.org/hoogle, fails as you have linked. Shame, but seems unharmful for now, and will go away when I put in a redirect.
Hoogle 5, the new version at http://hoogle.haskell.org/, refuses to connect to the server. No idea why. I'm not convinced it's getting as far as my code. If you have any ideas, please let me know.
Hoogle 5 locally works just fine, which is great news.
E.g. https://www.haskell.org/hoogle/?hoogle=%E4