I don't believe that it's an aquarist error if it's happened pretty much to everyone that's owned them. There isn't enough research done to really say what it's from. They could require different water parameters once they reach a certain size, it could be a breeding thing, change in diet, etc. It could be from anything, but whatever it is, it has yet to be replicated in the home aquarium. I believe it has something to do with how sensative scombs are to water conditions, in that if it doesn't match the natural conditions exactly they die. Where as other species of fish are more tollerant to a variety of water parameters. It's not a simple as an aquarist error, if it happens to everyone.