There was a cloudflare error while posting which triggered lots of folks to repost lots of things. The error came up after the post was saved, though.
No clue. What happened was...
i had noticed that a surprising number of people were posting the same things 2-3 times and assumed it was due to some non-obvious error. Then i posted something (must have been /item?id=38989363) and, indeed, got a CloudFlare error. My instinct was to tap Back and Submit again but the number of repeated posts i'd noticed earlier tipped me off not to. Instead i visited /newest and there was my post, despite the CloudFlare error.
<https://news.ycombinator.com/item?id=39002310>
(Sort of an anti-example of the problem, people's experiences may have varied.)