DateFormatter return nil in some case

Question

I have two date string str1 & str2. When I get date from str1, it works well. But with str2, it returns nil. I can't understand why.

let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'hh:mm:ss.SSSZ"

let str1 = "2019-04-11T12:01:43.694406Z"
let str2 = "2019-04-16T17:00:16.124653Z"

let date = dateFormatter.date(from: str1)

if let date = date {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy-MM-dd"
    let result = formatter.string(from: date)

    return result
}