I've seen this bug couple of times before, no big deal but I'm just reporting it here since it happened to me now on AU.
I wanted to upvote the first comment, it had 3 upvotes, clicked upvote, it says I could not upvote twice and the vote didn't show I tried 5 times nothing.
Upvoted the second one it worked instantly, the third one it worked too. Refresh the page and only then my vote appears on the first comment.
Some ajax glitch I guess no big deal but I'm just reporting it, not the first time, can't recall the last time, I'm rarely active these days, and not only on AU.