Have you heard of failure-to-thrive? This happens sometimes when a chick is not fully developed when it hatches. Internal organs are immature and function poorly. It can cause slow digestion, slow nutrient absorption, and very quickly this FTT chick falls behind due to weakness from lack of calories and nutrients.
The solution is to give the chick daily doses of Poultry Nutri-drench and high protein easily digested food such as finely minced boiled egg (white and yolk) or crumbled tofu.
If the chick shows signs of constipation, which is the number one issue with these chicks, give it a teaspoon of coconut oil slightly chilled so you can easily put tiny pieces of the oil into its beak. That will help get the poop moving and cut down the pasty butt risk.