Crested breed chicks dying for no reason?

We got an order in from Welp last week of 20 bantams, and 10 crested breed chickens.

First it started with mine - 2 of my crested silver laced polish chicks randomly died - they were fine when I checked them, but not 20 minutes later, they were on the brink of death. They looked like they had hope of living, because they were responsive. They just acted like they were tired, but then died 20 minutes later. This happened over the course of 2 days.

I talked to my neighbor today, who got 5 crested polish in this order (and 10 bantys) and said the same thing happened with one of theirs...

The bantams are showing not even the slightest signs of illness...
Any reason why it might be? I'm assuming its something to do with genetics in the crested breeds, but who knows?

Any info would be great!