New Hatchling Was Alive Now Dead-What Causes These symptoms???

We are hatching out 29 eggs today, 7 have made it out so far and were seemingly thriving except for one little one that kept falling on its back and not being able to right itself.

They all seem uncoordinated at first and we didn't think too much about it, all of the others could get back on their feet by themselves, though.

This one hatched out last night, early this morning, we put him in the brooder when he was dry and it seemed healthy and lively. He could walk, his head was held normally and he chirruped like the others. But, he did fall or get pushed over a lot. I had to help him back over 3 times and my husband did it once.

We checked on them often and in the space of 15 minutes, this afternoon, he went from upright and appearing fine to on his back dead.

This little bird did have what looked like a small bubble on his belly, we thought it might have been unabsorbed yolk sac and as it looked like it was reducing in size, thought it would take care of itself.

He came out of his shell on his own, but we did think that perhaps it was a pullet egg because it was very small comparatively. (These were eggs shipped to us-TX to NM). Could he have had to hatch because he outgrew his shell and there was no more room, but he wasn't quite ready?

Or is there some other problem that chicks can have that causes this? I have tried searching the forum for answers, but am obviously not choosing the correct wording, as nothing is coming up.

These are our first chicken eggs we have hatched.

Thanks!

Deb