6 day old chick suddenly not eating much and mostly sleeping under heat plate

[Mellowmalt]

hey peachy,
you know more than me since you actually have the problem, luckily I've never encuntered it so not thought about it much.
You are right it is a bone problem but the bones are still growing but maybe it cannot be fixed.

I saw a case of crossbeak in an article but looking at it there is no actual mention of crossbeak, just a picture of it and mentions that bone deformations are caused by deficiencies in certain vitamins so I dunno, Rickets is also caused by a deficiency in vitamin D and Calcium:

https://www.thepoultrysite.com/publications/diseases-of-poultry/220/slipped-tendon-perosis

The newly hatched chickens have depleted calcium stores. The calcium deficiency is rapidly manifested if they do not receive an adequate diet supplement. Clinically and morphologically, soft bones or various degree of bone deformation are determined. The birds usually lie down and their growth is retarded