If users give your post a "bad" rating, it can gain red stars, which basically mean the post has been rated negatively. The post will then no longer be visible if your threshold does not allow negative posts to be viewed. It's not deleted. You can still view negatively rated posts just by changing your settings.
Looks like some folks out there have been giving your posts negative ratings, and once they get a red star you or others can't see them anymore unless the forum settings are changed to allow it. I allow posts with up to 5 red stars to be visible, so I can see everything.