Ironically this happened while we are cleaning out our website. We run a country related directory. A problem that often occurs is that websites listed are no longer existing, and that the content of websites changes or the sites are redirected to inappropriate content.
Over the last week we noticed that our CTR dropped significantly. Initially we thought that our deletion of a few hundred websites had somehow confused Adsense and that we had to wait things out to pick up again.
Then we noticed that one of our well visited pages was not displaying ads anymore and when checking with the Adsense tool we got a message that ads where not available for the page with a few possible reasons listed, one being : contentious content. The page in question related to 'models and stars'. While none of the text of the links seems inapprapriate, it did happen that one site had become overly 'explicit'.
We can only assume that this was picked up by the Adsense Bot and since we where linking to that site, advertisements were discontinued on our page linking to it.
This is the first time I notice such a thing. Of course, we will now certainly continue cleaning up our directory and continue removing links to contentious content (that will probably be a continuing effort)
What is good however, that this was not a reason to ban us, and actually we did not receive any message from Google regarding this issue. So probably there are preliminary steps in Google's algo before they contact webmasters regarding content, and/or ban a site.
We decided to remove adsense code from the page in question. Possibly after a while (and if we are sure the content remains appropriate) we will add the code again.
Any similar experiences? Comments welcome.