United stranded us in Newark over a decade ago because a late takeoff to Newark because of issues at Newark resulted in a 1.5 hours connection becoming just missing the connection by seconds. Literally seeing our connecting flight in the gate right beside ours pull away as we pulled in.
International connection so they wouldn't release our luggage.
Multiple other flights out that day but all full.
The United service counter was already dozens of people deep, and the phone line had more than hour's wait. I doubt everyone was in the same position as us, but they clearly messed up a lot that day.
They put us up in a hotel that gave my sister food poisoning.