This what Apple Technical Support says about this (after paying $49 for a Developer Tech Support Incident):
These messages are coming from Core Location framework. The most likely cause of these messages is that there isn't a run loop running on the thread on which the CLLocationManager was created. (This implies that the CLLocationManager wasn't created on the main thread.) The messages that are being discarded are location messages: event 0 is a location and event 24 is an authorization status update, for example. Because the messages being discarded, you won't see the appropriate delegate callbacks being invoked. Did you set up a geofence or some other callback and isn't servicing it quickly enough? The queue limit appears to be 10 before it starts dumping events and logging this message. This information isn't publicly documented yet. I'm working with the Core Location team to improve the reported messages and see if this can be better documented.