DIAGNOSIS Those are likely uniformity issues, sometimes called 'dirty screen effect' or 'vertical banding'. It's a common panel lottery quirk in IPS-type monitors, where slight variations in the liquid crystal layer cause shadows. It's most visible on solid gray or muted colors.
FIX First, rule out the cable and source. Try a different HDMI cable and see if the lines change or disappear. Open a pure gray test image (search online) full screen. If the lines are static and always in the same place, it's the panel. You can try a gentle panel refresh: power the monitor off, unplug it from the wall for a full 60 seconds, then plug it back in and turn it on. This can sometimes reset the power to the panel and minimize the effect.
IF THAT DIDN'T WORK Check if it's related to a specific setting. In the monitor menu, go to 'Picture' and turn 'Sharpness' down to 50 or below. High sharpness can accentuate these subtle panel imperfections. Also, ensure 'Response Time' (in the 'Game' menu) is not set to 'Faster' or 'Fastest', as this aggressive overdrive can cause faint coronas or shadows.
HEADS UP If the lines are bright, flashing, or cover the entire screen in a pattern, that's a sign of a failing T-Con board or loose internal cable and is a defect. If the faint shadows are only noticeable on test screens and not during normal use (watching videos, browsing), it's considered normal for the panel type and probably not worth a warranty claim.