See the Apple subreddit, roughly 70 people commenting that FaceID is notably slower than when they first got it, suspiciously after the 11.1.1 upgrade for a lot of users too.
https://www.reddit.com/r/apple/comm...m_medium=hot&utm_source=reddit&utm_name=apple
https://www.reddit.com/r/apple/comm...m_medium=hot&utm_source=reddit&utm_name=apple
https://www.reddit.com/r/apple/comm...m_medium=hot&utm_source=reddit&utm_name=apple
https://www.reddit.com/r/apple/comm...m_medium=hot&utm_source=reddit&utm_name=apple