This is easy to check. Open a program, do nothing for about 10 seconds, and try opening multitasking. You are guaranteed to see a drop in frame rate.
A vivid example:
It would seem that this is some kind of OLED display problem in iPhone, but iPhone X has similar There is no “cant.”
Of course, this defect does not interfere with the majority, but it will be especially annoying for the “sensitive” ones. Some owners even managed to replace the smartphone with a new one, indicating an annoying bug. It just didn’t get any better.
The bug is present in all versions of iOS 12, including iOS 12.2 beta 4. Have you noticed? [9to5]