I've seen it happen at least once in the few years that I've been on Hacker News, see https://news.ycombinator.com/item?id=17228704

I got a server can't respond to your request type message this morning. OK, the server wasn't down, but it was loaded enough that it couldn't serve me. A page refresh and it was working.

Here's the official status twitter: https://twitter.com/hnstatus