I have recently noticed what looks like a "coffee stain" on my IPS monitor. It is hard to describe, but if you imagine the stain that coffee would leave on wood after its dried, its a bit like that, and can only be seen when the monitor is either off or the screen is black in that particular area. I have tried gently running my finger over it and it appears to be inside(?) or behind(?) the screen and reflects light. I was wondering what this could be. Image below.
https://i.imgur.com/r0yF4HQ.jpg