It happened on my iPhone 6, and now it's happening on my iPhone 8 Plus. I will be in bright, broad daylight, and suddenly the display dims so I can hardly see it. I go to the Brightness controls, and they only change the brightness from 0% ~ 50%; from the halfway point upwards, there is no change in brightness. I have tried everything short of a wipe and reinstall. I have set all the the usual suspects—No True Tone, no Night Shift, no Zoom, no Color Filters, Invert Colors, Auto Brightness, or White Point. It's all turned off. And yet the danged thing still goes dark, stays that way for several minutes, then brightens up—never with any external input. I do put black electrical tape over the front-facing camera. However, I don't see how a permanent light block could cause erratic light changes. Any ideas what's up? Any suggestions? Thanks!