I don't know what changed lately, but recently I have the same issue with iPhone 5 screens.
I repaired many iPhone 5 screens but since a couple of weeks i'm seeing this issue more often. I put the iPhone on a charger at sleep and in 90% of the cases the problem disappears after like 30 minutes... Just leave it for a while. Hope this helps for you.
Good luck!
Johan
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== Update ==
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Hi Guys,
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I was used to turn on the phone and test the screen when the iPhone 5 was still open, so I didn't had to open the phone again if (for example) the sensor didn't work. Last couple of weeks I totally install the screen and close the phone before turning it on. Fingers crossed, but so far I didn't had these issues again. I think thats the solution.
I don't know what changed lately, but recently I have the same issue with iPhone 5 screens.
I repaired many iPhone 5 screens but since a couple of weeks i'm seeing this issue more often. I put the iPhone on a charger at sleep and in 90% of the cases the problem disappears after like 30 minutes... Just leave it for a while. Hope this helps for you.
Good luck!
Johan