There was some plane at Frankfurt last year that they had folks boarded for a flight to leave, and then deboarded everyone when the plane had issues (they shut the airport down at 11 PM for quiet hours, and resolving the flight was impossible). So they took everyone to some hotel, and brought them back around noon of the next day, and then waited another four to six hours before that international flight could finally take off.
I waited three hours on the plane in Frankfurt one time. Never found out why.
This is much more common for international flights than you would think. Those long trips typically just wait until the next regularly scheduled day. Even then most passengers are rerouted on other flights and carriers.