It is how the logo is. It is supposed to be the lighting. Look at the logo at the top of this page. See the line. That is what they tried to make it look like but it has been mentioned since day 1 of original iPhone that some think it is a flow in the screen when it isn't.
It has always been there. Every so often someone writes in worried about it. It is an attempt at shading for depth. There is nothing wrong, it is normal.
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LINE THROUGH THE APPLE LOGO
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