Ask HN: Why did my “Show HN” post disappear?

It seems my "Show HN" post disappeared for some unknown (to me) reason. I can still see it there when I'm logged in, but it seems to be gone when I sign out (and I suspect other users aren't able to see it either).

As far as I can tell, I didn't violate any of the rules; I re-read them just to be sure it wasn't my mistake. I'm not trying to spam, and just wanted to share something I made and thought others might be interested in, so it would be nice to know what happened and how I can avoid this next time. Thanks!