Also worth noting...again totally guessing here about it being fatty liver.
"Fatty liver disorder also impairs calcium metabolism in the bird, thus affecting skeletal integrity and eggshell quality."
We can all guess til we are blue in the face.
Keep this link handy just in case.
Might be...
Just a guess but something worth noting:
"Likewise, feeding rancid fat can cause liver hemorrhage, again without fat accumulation."
I don't compost so I am unsure if there is rancid food in a compost pile or not...
I am sorry for your loss.
If you lose another I highly recommend sending it for a necropsy.
Fatty liver disease kills with no signs or symptoms.
What exactly do you feed your flock?