It's not super common. There are 2 types, hereditary and nonhereditary from what I know. The nonhereditary is from injuries or bad incubator settings. But usually you can't tell if it's hereditary or not so you just don't breed any with crossbeakNo it isn't. Not as common as what happened with you. That is really sketchy.
I have a flock of 23. 6 were hatched on my own, the rest were from hatcheries both directly and indirectly. 16 were directly from a hatchery and we picked up a few from people who were moving. Out of a flock of 23 none have cross beak.
6/6 that I hatched also do not have it. Either I was extremely lucky, or it is not very common.