sick chickens, help!
Welcome to BYC. The new chickens may have been carriers of some disease, possibly a respiratory disease since you describe eye drainage. If you lose another chicken, I would contact your state vet or veterinary college to do a necropsy to find the cause of death. Respiratory diseases include MG, ILT, coryza, infectious bronchitis, and others. Have you seen any coughing, wheezing, nasal drainage, lameness or other symptoms? Sorry for your loss.