I'm working with a site that started showing all PSA's on Nov 7th. We didn't make any site changes, and it had run for about 2 years at consistent traffic and revenue levels (350,000+ daily pageviews, all organic/type-in)
Google is unresponsive to the 3 requests I've made through the adsense contact form, and we really don't know if its an issue with the adsense code block or the site content, or something else entirely.
The site is a social community, so content is all UGC, but the type and mix of content hasn't changed substantially over time. If there is something offensive I would have expected PSA's to show on those pages, no?