That iPhone X you're holding, yes, it could have a serious issue. Apple's sophisticated 3D-sensing facial recognition system, Face ID, is one of the signature features of the iPhone X. As it turns out, however, Face ID has some issues that Apple has now confirmed. The iPhone maker has authorized its own stores as well as authorized service providers to repair or replace any and all faulty devices.
What's interesting here is that the repair process for faulty devices doesn't even include the Face ID system, rather involves repairing the rear camera. Pretty strange, isn't it? The TrueDepth camera system inside the iPhone X notch is makes Face ID possible.
If you have an iPhone X and are experiencing Face ID issues, you should take you handset to an Apple Store or an authorized service provider where they can take a look at the issue and appropriately fix it.
The first step into repairing the problem is by fixing the rear camera. According to an instructions copy obtained by MacRumors, here's what it says:
In order to provide the best customer experience, if a customer reports that their iPhone X is having Face ID issues, you may be able to resolve the issue with a rear camera repair. Run AST 2 on the customer’s device to check the camera. If the diagnostics find issue with the camera, perform the repair to see if the issue is resolved. If the issue is not resolved, perform a whole unit replacement instead of a same-unit display repair.
At this time, we don't exactly know how this issue is linked between the front and rear camera systems, but it appears that the issue may be with the dual-lens camera on the back that might be causing problems with Face ID functionality. If the repair of your iPhone X doesn't work, a full-device replacement is likely to take place. While this issue doesn't appear to widespread, you should have your iPhone X looked at if you've experienced Face ID problems recently.