A bug concerning AdSense page view counts has been discussed here and on Google's forum for years without an official response (to my knowledge). I noticed that a Google employee recently spoke up about this, so passing along as an FYI:
Essentially, only the first ad unit on a page triggers a page view. Thus, if you have two ad units on a single page (header and footer) and look at channel stats for the second ad unit, it will report zero (or nearly zero) PAGE impressions while the ad unit impressions, clicks, etc. are correct.
Previously this only impacted custom channels. Now that the new AdSense interface includes reports for ad types, ad sizes, bid types, targeting types, and ad units, the impact of inaccurate page view reporting is much more widespread. Google has switched the default view to ad unit impressions instead of page views to mask the problem. It sounds like they're open to other suggestions. Without significant backend changes on their end, it seems the easiest solution would be to remove the page view metric from the impacted report types.