In brief: Early versions of operating systems usually come with a warning that users may encounter bugs with varying degrees of seriousness. The one found by some users of Apple's iOS 15 beta is definitely on the far end of the 'bad' scale: it's stopping Face ID from working.
User reports posted on Reddit and Twitter (via MacRumors) state that the iOS 15.7.1 Release Candidate released earlier this week is preventing Face ID from working on devices that include the iPhone 12 Pro, iPhone 12 Pro Max, and iPhone 13 Pro.
One Redditor says that attempting to reset Face ID on their iPhone brought up a "Face ID Is Not Available" error, rendering the security feature completely unusable. A Twitter user who encountered the same issue is advising people to avoid the iOS 15.7.1 Release Candidate entirely.
MacRumors notes that iOS Release Candidates usually end up being identical to the final iOS release versions, but it's possible that Apple could launch a new iOS 15.7.1 Release Candidate before the operating system's final incarnation arrives next week.
Some users who found iOS 15.7.1 borked their Face ID say there is a solution: download and install iOS 16. As to why people haven't simply jumped straight to Apple's latest mobile operating system, many are put off by the number of problems that users have encountered since its release.
One of the biggest issues with iOS 16 was the camera shake. In September, iPhone 14 Pro owners were posting videos of their device's cameras exhibiting strange behavior when used with third-party apps. The camera module's movements were so violent that they caused a buzzing/rattling noise.
Apple fixed the vibration issue with the release of iOS 16.0.2, but there have other problems relating to FaceTime and iMessage. They've also been addressed, but a lot of iPhone users remain wary of upgrading until the operating system is more stable.
There's also the issue of compatibility. Some devices are not compatible with iOS 16, including the first-gen iPhone SE and iPhone 6s/6s Plus, meaning people can't upgrade to the latest version.
In other Apple news this week, reports claim the company has cut iPhone 14 Plus production by up to 90% on the back of weak demand for the larger non-Pro handset.