Q: is the gray line there no matter what is being displayed?

I would guess it's likely a hardware failure in the LCD module, more specifically one of the outputs of the LCD row drivers, as I described in my answer to a similar question

unfortunately it's unlikely you'd be able to repair this yourself without replacing the whole LCD display module.

one thing to try - does slight pressure directly on either edge of the glass where the dead line is bring it temporarily back to life? - that might mean it's just a physical break in a connection of one output. bad news is it's likely impossible for you to resolder, the drivers are often bonded directly to the glass.

I apologize for the terrible picture quality. The line is between "backlight" and "brightness". It isn't a crack in the screen. Thanks for the responses.

On a side note:

Any idea what causes this issue?

I have the same problem with my ipod classic. My line is around the bottom third of the screen and now stretches 3/4 across the screen and is thicker in spots.