Are they all the same breed? If so are they a breed that tends to be sold out a lot? It could be they're somewhat over-bred and the genetics are weak.
I say this because my cream legbar hens I got from one particular hatchery seem to be prone to health problems: I've had three die prematurely over the last two years.
I also had a cockerel (blue cuckoo maran) that I had to put down at 5 months old due to terminal cardiovascular problems. They've sinced discontinued that breed at that hatchery.
Even if there's not some inherent issue with the breed, I've noticed that if you have a dip in temperature or humidity or some other mishap during the incubation process at the wrong time, you can either lose most or all of the hatch or you'll suddenly get a profusion of health problems or deformities. One time I had a power failure about a week before hatching day with a clutch of guinea eggs. Most didn't hatch, but I had 5 healthy-looking keets emerge. Initially they seemed fine but they started getting more and more lethargic and within 10 days they all died. From the symptoms it looked like maybe their lungs didn't develop properly and the larger they got the weaker they got.
If I can have 5 problem birds out of a batch of two dozen, it's no stretch of the imagination that a place that hatches thousands of chicks a day could have sent you a batch of "duds" by mistake.
I wouldn't pay $360 for whatever an "implant" is, even if they claimed it to be 100% effective. These are animals that often don't live more than a few years even if you're doing everything right: predators, bird flu, even just dumb accidents and they're gone. There's a reason why their reproductive strategy is to produce mass numbers. That implant could work fine and then one night they'll fight over roosting space, and one of them gets knocked off the roost and breaks her neck.
If it was me, I'd make them as comfortable as you can, double-check to make sure that you're not doing something wrong or if there's not something weird in your soil or water that's affecting them, and if the worst happens and they all end up having problems I'd have to decide if I'd want to risk going through all that again and if so do I go with a different breeder or breed.