Ask HN: Glitch when posting new comments?

I posted a comment but it didn't show up. I tried a few times more and then gave up, thinking it was a problem on my end. A while later I checked my history and saw that I had actually posted it multiple times. I also see that the same must have happened for other people, for example at https://news.ycombinator.com/item?id=8827072

What's going on?