For ORD, it appears the SCHEDULED DEPARTURES are not being “activated” once they depart. I click on a flight that was scheduled to depart 2 hours ago, and see there is another flight track displayed above the scheduled one.
I don’t work for FlightAware (although I wish I did) or know anything about how FlightAware works, but I’m guessing it has to do with the tracking outage. I’ve noticed this on many airports.