Three months ago I noticed a small gray stain in my macbook pro screen (2017, touch bar, 13''). First I thought it was...

My Macbook Pro 13-inch 2017 touchbar model also started showing this issue around two months ago. I did not take it to repair service (and now, with COVID-19 pandemic, it will probably take longer to do so), and I've been closely monitoring it to understand what might be happening. I wanted to share what I learned: (1) As others are saying, when the computer is left resting (lid closed) for enough time, the lines disappear. (2) The lines might appear after some time using it, but this will depend on what type of task you are doing. Simple tasks usually do not trigger the heat issue and I can use the computer for hours without seeing them. What I observed is that any task that requires VIDEO PROCESSING (and here I'll guess that means GPU use) will make the problem pop up very fast. Watching any videos, for instance, will trigger the problem after a while. (3) Once the problem starts, it will get worse and worse until you close the lid and leave it to cool down. Until now, the problem completely disappeared...