Hardly a days goes by that Google doesn't restrict ad serving on one of the articles. In some cases it seems to be temporary, in others it may be permanent.
As you may know, Google is very sensitive as to what content may be shown on a page in order to be considered for ad serving. "Offensive" items could be anything deemed shocking, scandalous, gory, sexual, tobacco or alcohol related, and so on.
It doesn't even need to be an article about those topics; sometimes the cover art of a featured book is enough to trigger ad blocks. I've also seen cases where I couldn't find anything wrong with the page except for the fact that some embedded videos were no longer valid. It's a good idea to revisit pages from time to time and make sure all the links, products, embeds etc. are still working.
We don't really have much of a say in it. In the interest of everyone here who wants to use Adsense, we did however, on occasion, disable ad serving on pages that were obviously running afoul of Google's sensitive nature.