Apple sends document to authorized service providers telling them how to deal with Face ID issues17
Apple has reportedly sent a document to authorized service providers outlining what they should do when an iPhone X owner has issues with Face ID. The first step that Apple recommends is a diagnostic test to see if there is a problem with the rear camera on the device. Wait! We know exactly what you're thinking; doesn't Face ID have to do with sensors found on the front-facing TrueDepth Camera? And you'd be exactly right. However, there does appear to be some connection between a rear camera failure on the tenth anniversary model, and the failure of Face ID to work correctly. Why the rear camera? According to a Reddit user who had a problem with the Face ID feature on his iPhone X, the guy at the Genius Bar told him that the rear facing cameras are connected to the TrueDepth Camera.
If the diagnostic test doesn't show any damage to the rear camera, Apple has instructed the service providers to replace the user's iPhone X for a new phone. And the steps that authorized service providers are being asked to take (diagnostic test first) also applies to the Genius Bar inside Apple Stores. The company says that it is requesting that the test be done "in order to provide the best customer experience."
The document was obtained by 9 to 5 Mac and puts into writing Apple's request that the rear camera be checked out for a Face ID issue before a new Apple iPhone X is given out as a replacement. Just yesterday, another letter from Apple to authorized service centers was leaked, revealing that Apple is aware of a problem with the iOS 11.3 update that broke the microphones on the iPhone 7 and iPhone 7 Plus.
source: 9to5Mac, Reddit