Small line on the top left corner of the screen

Hello. Recently i've noticed a small line in the top left corner of the screen on my J5. It is not a scratch, doesn't affect display or touch and can only be seen at specific angles. It has doubled in size in few days after i've first noticed it. Phone was never dropped or damaged, it's been mostly used in an office environment.

What could it be and is it an easy fix as i wouldn't want to send it to service to be thrown around for 30 days. Still in warranty though.

Pics:

i.imgur.com/SmDzUDd.jpg

i.imgur.com/xZNLe2W.jpg