In two separate occasions my Dusk Crusader got killed by a normal attack despite having much more defense than the enemy’s attack (20k versus 700 attack). I inspected the creature and it didn’t have any trait that could cause that. I checked battle history and it was a normal attack (no traits nor minion). Also no realm properties that could have caused it.
I am not sure if it’s bugged or there are some reasons why an enemy can damage you despite it having much less attack than your defense.