Update: we've now fully identified the cause of the problem. We also identified how it snuck past the check we had in place to prevent this very thing from happening
We've tested our update and believed it to be sound, but just thought of a reeeeally subtle flaw that we want to correct before we run it. To let you know the kind of details that give us a headache, if we hadn't caught this subtle problem, it might have allowed pitcher stats to count for yesterday for players that switched leagues in leagues that are AL or NL only where the player should no longer be allowed to accumulate stats. Sigh. So that is being covered, and updates will start shortly.