On a serious note......I happen to notice that my LB's eggs have HUGE yolks. I had one chick hatch from one of her eggs and the size of this chick's belly was just ridiculous! Same thing, she couldn't walk because of that belly. She was like Violet in Charlie in the Chocolate Factory after she blew up like a blueberry.
I imagine it's because she absorbed that HUGE yolk just before hatching. So, that could be your answer.