There's a lot of debate over whether or not this is a software or hardware issue (happens on some pixels straight out of the box) every update since August has claimed to remove the issue but there are still reports of it remaining.
While pixels do need to be calibrated after screen repairs, this is usually just for the fingerprint sensor.
Turning off screen smoothing should reduce the effect, however in order to fix it you'll need to either replace the screen again (hoping it is a hardware issue) or wait for another update (hoping it's a software issue).
I wish there was more advice I could offer here, but it's a widespread yet overlooked issue.
Coco,