I can confirm, HN, GitHub and Slack are very slow for me as well. Google is very fast, on the other hand.
From wiki: the thundering herd problem occurs when a large number of processes or threads waiting for an event are awoken when that event occurs, but only one process is able to handle the event. When the processes wake up, they will each try to handle the event, but only one will win.
The DNS entries should be cached by the browser (and the middleware), so that this problem should only happen once, but I get this constantly.
Also, I sometimes get an error message from HN, which seems to indicate that this is some backend issue which fails gracefully with a custom "We're having some trouble serving your request. Sorry!" on top of a 502 code.
It feels more like there is something else still broken.