It's most likely a heat issue; take a look at these pictures:
https://fjallfoss.fcc.gov/prod/oet/f...ive_or_pdf=pdf
If you go down to page 20, you can see what's hidden under that buldge in the plastic casing you can see on the back of the screen when you slide open your phone.
That chip may be the controller for the backlight or any number of other things; the FCC failed hard when they didn't take a picture specifically of the chip and what looks like a LIP or ZIP connector.
End result, it's a hardware flaw. Now the game is, how long will they lie and bull**** everyone with the mantra "It's not a common problem".
