White rectangle (bar) top left of screen

[RemarkablyAverage]

I have a small white rectangle at the top left of my steam game client. The game plays fine other than that. The rectangle gets longer and shorter like an active bar graph. I have changed the visual settings and updated my drivers/verified integrity of game files and still the problem persists. It does not happen if I play the game through chrome.

[MarvinTMB]

I've also experienced this, I think only with the desktop client.