Okay, very weird error here. Even weirder since it started happening on both my blogs at the same time (everything was fine earlier today).
So I'm on the dashboard, I can see the "preview" or the "mini view" of the Site Stats just fine. I can click on View All and get the usual site. However, when I click on a single day (clicking on the respective bar in the stats graph), I am taken to the respective blog's 404 error page.
Everything else is working fine on both blogs. Both are using 3.3.1, by the way, and both getting the stats through Jetpack 1.2.2.
Stats are still being collected, as I can see in the "mini view" and the stats dashboard. I just can't get to the detailed daily view.
Does anyone have an idea what could cause this?