I have the same problem. Since March 17th (thursday last week) all my sites in Analytics started to show only about 50% of the actual AdSense pageviews and earnings.
Normally it is about 5% ~ 10% lower.
Last week Google implemented the faster AdSense ads (that's what they wrote on their blog):
And since then Analytics is out of sync with AdSense.
Perhaps the maintenance yesterday solved this problem.