AW3225QF, rectangle pops up when pixel refresh?

Hi everyone!

I've been noticing that after a pixel refresh, a rectangle pops up on the screen. You can see it while gaming as well. I've tried turning it off and then back on but it didn't work. It only goes away when restarting my pc. It's like a rectangle water mark. Anyone knows why this happens and how to fix it? Unable to upload an image.