Missing Recent Post (random)

When I add a new post to my wp site, most the time the recent post slider updates and shows the most recent posts. Then once in a while, it does not show a recent post. Ignores some of them. What cauases this?
I don’t have anything set up. It’s all categories. I have no “exclude” set up.
I see that it’s a couple categories that are “missing” from the slider.
http://wordpress.org/plugins/recent-posts-slider/

Never mind. Close.