2nd hen deteriorating after 1st suddenly dropped dead?

[fuzzyfarmer]

Hello! I currently have a mixed flock of egg-laying hens that I got at the same time from the same hatchery (mostly red sex link, a few Sussex white and poule noir). A few days ago one of my reds was mostly hunched in one corner of the coop and didn't move much or seem interested in food. All other birds seemed perfectly normal. Checked her for parasites, wounds, etc - nothing evident except pale comb and small cuts on her comb because the coop bully took advantage of her immobility to peck on her. Treated the wounds, put her in the old rabbit cage to keep her safe from bullies with some food and water. The next morning she was dead. Still couldn't find any evidence of why. Figured maybe it was a freak occurrence/5% mortality/she found something bad in the run and ate it. Then this yesterday evening I noticed one of the noirs acting the same way - low energy (but not completely immobile), not diving in for breakfast. Checked her out too - no obvious problems with vent, parasites, wounds... What am I missing??

The only thing from Storey's that seems like it could be a match for the symptoms is septicemia or liver worms?
Otherwise of note: this batch of chickies has had a lot of vent prolapse problems, which makes me think they have bad genetics.

Gotta run to doctor appointment, will add other standard details when back but would love anyone's ideas in the mean time!