This sort of failure can sometimes be caused by an intermediate DNS server failing: You only actually see a problem if all of the caches closer to you have expired. Repeating the request might pick a different chain of DNS servers, which will allow your local cache to populate and work correctly for some time.
As this whole process happens before any IP connection is actually initiated to the desired server, it’s relatively common for timeouts and other safeguards to have not started, resulting in an infinite wait for a reply that isn’t coming.
Being old fashioned when I visit users.rust-lang.org I expect every byte I receive to come from users.rust-lang.org. After all, it is supposed to be a secure connection. How can that allow for getting whatever junk from intermediaries? How can it be that I don't really know who I'm connected to?
Anyway, Chrome and Firefox displayed the forum for a couple of days on the same Mac M1 when Safari did not. How is that?