My iPhone has been free of this issue until a few days ago. When at 50% brightness or less, the animation when locking my phone had a weird stutter to it. Hard to explain, almost as if it goes from on to dark to very dark to off. I can’t unsee it. I’ve done a restore already and that didn’t help. The weird thing is, there is no stutter if I don’t go to the home screen. If I just wake the screen and then lock it, I don’t get the issue. Very bizarre.