I was just wondering what kind of things would cause a bag to miss a flight when it is checked in 1 hour 30 minutes prior to departure from DCA to DAL on a single segment?

We sat around the baggage claim and waited 2 hours for the next flight and it arrived but it was just 1 of my group's 9 bags that didn't make it. There were others in the baggage office from this same flight.

They just had us fill out a report but no one suggested we wait for the next flight. We did that on our own. When we told them the bag arrived and to cancel the report, they did offer a $100 voucher.

Could it have been a weight restriction departing DCA or just a mess up?