Chicken die spontaneously around 4 months

[Cartar]

I'm fairly new to chickens
I've had two different groups of chicks do perfectly fine and then they all die so about 4 months old
Any suggestions??
If I get adults, they do perfectly fine

 

[lazy gardener]

Where do you get your chicks? What breeds? What do you feed your chicks? Have you paid attention to the mill date on your feed bags? How and where do you store your feed? Do you allow them to eat all they want, or do you feed them a set amount every day? How do you house them? How do you brood them? What size coop and run, how many birds? Have you had your soil tested? Have you had your water tested? Do you give them grit, starting at what age? What is your general location? What time of the year do they die? Temperature max and minimum around this time?