My Galaxy S4 mini was doing that and it seems to be due to the battery either the lithium battery discharges from being totally unable to detect its own charge levels anymore or the built-in device battery finally gone bad. If you can find one, share your info, i am looking for a good s4 mini to use the good batteries/parts, to see if it solves the issues, because I love that phone and the camera enough to keep it running despite it being no longer supported and the dwindling of available apps, but i cannot spend money on this project. I finally bought refurbished Galaxy S7 on eBay 6 months ago, my regrets are plenty and quality of Samsung phone 11 years newer it's not anywhere near as good. Disappointed!
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I have this exact same issue with my Galaxy S7, the shaded area of the screen isnt black, its just darker, and covers about 3/4, the rest appears as it should be. Seems to always be right after my phone was charging, but it has happenend when its 100% & unplugged. The flickering starts - happens rather its plugged in or not - the screen is jumpy & brightness is glitchy, then it causes the screen to have the shaded area afterwards-always just on only one part of the screen. It seems to happen totally randomly when it comes & then it disappears without any real reason. So without any consistent triggers or any repeat of situations that would explain it makes it impossible to pinpoint any cause - I cannot fix it, if I can't make it repeat the incident or know what causes it.
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