
Update (6/6 9 am PT): Blizzard reported another issue with authentication servers a little after midnight PT, which was shortly after I started timing out (see previous update), and then reported again that they were fixed at around 5 am. I was able to log in without issue this morning.
Update (11:30 pm PT): Blizzard said on Twitter that the previous login issues have been resolved, but when I tried to play Diablo 4 just now, I got a timeout error: code 300008. (See screenshot above.) We'll update this story when we learn more.