Sometimes, it could be the genes or nutrition of the parents. Feed has really gone up this year and maybe, there has been subsitutes.
Don't use sawdust or shavings the first week, they will try to eat everything. I use a Rubbermaid for my babies and use old towels for a week. Also Dave Holderread suggest you give greens right away in water, tiny bits of lettuce or grass. Regular light bulbs a 60 or 100 is usually enough, make sure they can get away from the heat , and they will find their own sweet spot. I have gotten birds shipped 4 times from Holderreads in Washington or is it Oregon to Georgia and only lost 2 out of 45, and they sent an extra each shipment. I added the sugar too, for a day or two as his book says. Ducks are very sensitive to poisons or toxins, so who knows what may have happened in shipping. Ducks don't need all the vitamins and suppliments chickens get.... they are much hardier.
I suspect it may have been either something wrong at the breeders end, (anything from messed up food, to mutations, poor breeders perhaps, illness) or from the shipping. Holderreads puts your Phone # on the outside of the box , so they can call you when they come in to P.O. Also, he suggest you tell you P.O. you are expecting live birds and to call you right away. I have gotten up at 4 am to 'wait for the call' , and went right away, but they were there for a couple hours.
A tiny sprinkle of brewers yeast or niacin, if they are defiecent , but that usually shows up as weak legs a little later, also mashed green peas can provide it too.