It was first reported December 13th at about 8pm (EST). In short, the numbers are simply not sorting correctly.
On my "Overview" screen, when I click on "Top Channels" it is not sorting by "Earnings" as usual. I can't detect a sort field by the data presented, it seems either to be unsorted or sorted by channel-id or some other hidden field.
Ashley, a Google AdSense rep said:
Thanks for reporting this issue.
I have forwarded the information you provided to our engineering team for further investigation. They are working to resolve this issue as soon as possible. Thanks for your patience,
We currently don't have an ETA on when it will be fixed.
Update: Google informed us that a fix will be coming in the "upcoming weeks." Seems pretty far ahead.