If your conditions are the same as they've always been for previous broods, there is clearly some pathogen at works.
It sounds like it came to your place with the hatchery birds. That doesn't mean it came from the hatchery. The chicks could have been next to chicks on the plane or in a sorting facility from somewhere else that had an infection.
It sounds like it came to your place with the hatchery birds. That doesn't mean it came from the hatchery. The chicks could have been next to chicks on the plane or in a sorting facility from somewhere else that had an infection.