Possible cause of 5 week old

[Gammas Bearded Babies]

I have a customer that purchased several chicks from me a week ago and they have all been doing great!
Then yesterday ONE was just sitting around and not joining in with the others as it normally was and then in less than 24 hours dead.
I'm trying to determine what might have caused this as I have never had any die past a few days old before.
I have the other hatchmates and they are all just fine. The customer also has 2 others from same hatch and they are fine.
Any thoughts?
Anything I should be askin customer?
Thank u in advance for your help!

 

[coach723]

There are so many possibilities. First thought would be coccidiosis, did they see any abnormal droppings? But knowing nothing else, it's really guessing.

 

[SandyRiverChick]

I had a case of Coccidiosis at 5 weeks. Definitely ask the person if he noticed red/blood in poo and if so, advise to treat the others with Corid asap. I noticed signs in 1 out of 5, caught it early, followed great advice from coach723 and all are well, now 13weeks.

 

[Gammas Bearded Babies]

They have quite a few and said they noticed nothing other than the lethargic and sitting alone.
I hate it but I have never had any problems with any of mine past the initial 3 days of hatching.