This is usually caused by hairline fractures on the LCD display which is the inner layer of the screen under the glass.
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In some rare cases there might not even be noticeable cracks and the fault is caused by just dropping the phone.
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Try shining a flashlight on the screen and look for cracks in the inner layer of the screen. The hard to spot ones are mostly at the corners of the display.
Clean your screen before hand with a microfibre cloth so that it is easier to spot.
Try shining a flashlight on the screen and look for cracks in the inner layer of the screen. The hard to spot ones are mostly at the corners of the display.
Clean your screen before hand with a microfibre cloth so that it is easier to spot.