In speaking with The Verge ahead of its iPhone XR review, Apple acknowledged the issue of “BeautyGate” for the first time. Apple is planning to address the issue in the upcoming iOS 12.1 update.
BeautyGate began when iPhone XS and XS Max users started noting that selfies captured on the new smartphones were applying a skin-smoothing effect or “beauty filter,” resulting in photos that looked quite different from those taken on the iPhone X or earlier iPhones.
According to Apple, the Smart HDR system is choosing the wrong “base frame” from the several exposures it takes and composites into a single final picture. Instead of taking a sharper, shorter-exposure image as the base frame, it chooses one with a longer shutter time, thus making the final composite image less sharp. This explains why the strength of the effect varies from one test to the next (as the amount of blur on the longer-exposure shot would vary), and why we see the problem on the iPhone XS but not the iPhone X (which does not have the Smart HDR processing system).
Apple says this will be fixed in iOS 12.1; going forward, the Smart HDR system will choose the sharpest frame as its base image when using the selfie camera.