What is this lump??

[Chicken poppy]

Why are the feathers missing

Judging off the photo, thats a newly hatched chick with all the feathers not fully fluffed. Soon the chick should become quite fluffy and it should fill in.

When chicks hatch they look rather wet and naked, its totally normal.

 

[rosemarythyme]

Why are the feathers missing

They're not, the crop is so big from food that the skin is stretching around it. As they eat it swells up, when they stop eating (i.e. overnight, assuming they have complete darkness at night) it'll go down completely.

 

[Sussex19]

Why are the feathers missing

They're not, the crop is so big from food that the skin is stretching around it. As they eat it swells up, when they stop eating (i.e. overnight, assuming they have complete darkness at night) it'll go down completely.

This!
It is 100% normal for a chick to appear to be missing feathers around the crop, as those little hungry babies eat so much it stretches, and also at that age their feathers may be lagging behind their development a bit.
As long as it does go down sometimes, (like at night when they dont eat) then there is no problem at all.