I am having the same problem, and it started about a week ago. The stats on the dashboard don’t match the site stats page and when I go to stat summary, they don’t necessarily match either of the first two.
I have loved the plugin and I have never had a reason to doubt the numbers in the last year, but now I’m starting to lose faith…or getting an inferiority complex.
Good thing I am going on vacation for a week. Maybe the stats will be fixed by the time I get back.