Some iPhones that have had their displays repaired or replaced by third-party technicians have become non-responsive because of an Error 53, which forces a boot loop on some repaired iPhones rendering them unusable. Here's Apple's clarification.
"We take customer security very seriously and Error 53 is the result of security checks designed to protect our customers. iOS checks that the Touch ID sensor in your iPhone or iPad correctly matches your device's other components. If iOS finds a mismatch, the check fails and Touch ID, including for Apple Pay use, is disabled. This security measure is necessary to protect your device and prevent a fraudulent Touch ID sensor from being used. If a customer encounters Error 53, we encourage them to contact Apple Support."
The problem with Error 53, from a user's point of view, is that it renders the iPhone completely useless (not just TouchID and ApplePay), seeing nothing but the Error 53 alert isn't just puzzling to most users, it doesn't help in any way.
Source: Engadget