Several things could have happened. There could have been an obstruction in the barrel, the round could have been flawed and not released from the shell properly or stuck in the barrel. The round may not have been seated in the breach correctly. There may have been a flaw with the bullet casing. Or, there may have been a flaw with the gun itself. (or a combination of some of these.0
either of those could be the cause. I would not rule out someone not checking closely and loading with ++ loads.
There wasn’t an obstuction in the barrel. The barrel isn’t damaged.