When this report in the admin dashboard has lots of data ( > 75 days of activity), the dates were ordered incorrectly. This is apparently expected behaviour; when using GROUP BY without specifying the ordering, PG decides to order, and it so happens that it works under some conditions but not others. Explicit ordering fixes the problem.
However, because this works in some conditions but not others, we can't really add a useful test.
Penar Musaraj
David Taylor
Mark VanLandingham