"The post was killed by software, user flags, or moderators. [...] If you see a [dead] post that shouldn't be dead, you can vouch for it. Click on its timestamp to go to its page, then click 'vouch' at the top. When enough users do this, the post is restored. There's a small karma threshold before vouch links appear." [0]
Right, but that doesn't really answer my question. The stories appear harmless and so many are flagged it has to be automated. So presumably it's software driven. But - why? With political or contentious topics it's usually obvious why stories go dead but for /shownew it's not.
[0] https://news.ycombinator.com/newsfaq.html