Some people have reported malfunctions with Face ID on their iPhone X. Most of them have blamed not wearing their glasses or hat, but this isn’t correct nor fair to the performances of Face ID or the iPhone X.
If you’ve been having troubles unlocking your phone, you’re likely to be placing it too close to your face. The software will recognize you whether or not you’re wearing glasses or hats: it’s programmed to learn to recognize you in different situations, despite what you’re wearing or the fact you might have a new haircut.
Another thing you might be doing wrong is: trying too hard. You don’t have to find an angle, or a position. All you need to do is pull up the phone as you usually do, look at screen as you always do when using your device, then swipe.
Face ID is a way better feature than Face Unlock: it’s not faster, but that’s because it is a lot safer. There’s a good reason why Face ID can be used to authenticate payments while Face Unlock can’t.