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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?
If none of the above, try generating new ad code
Also try using the ad code on another domain for few days to confirm that nothing is wrong with your account.
Otherwise wait for a reply.