There are many dermatologic diseases that will kill transplanted hairs. Most of these diseases have signs that are present, either obvious ones like alopecia areata or subtle ones like Frontal Fibrosing Apopecia, easily picked up by a doctor who is an expert in this field or a dermatologist who specializes in diseases of the scalp.  The key to avoid this is to have the diagnosis made in advance, something that an experienced hair transplant surgeon will ALWAYS  look for