Didn't realize at first that something was wrong, because a) I wasn't very familiar with Coredata, just inherited the code to be upgraded and b) I created my own caching on top of CoreData to compensate some issues with CoreData. Then found this error buried deep into console logs:
CoreData Error Domain=NSCocoaErrorDomain Code=1570 "The operation couldn’t be completed. (Cocoa error 1570.)
