Several customers, or as MacRumors reports, at-least 25 users have shared photos of the potential hardware defect across the Social Media and the Apple Support Communities. Though it is a small percentage of devices, but the issue seems to be increasing with time.
— mix0mat0sis (@mix0mat0sis) November 7, 2017
— Lejia Peng (@fanguy9412) November 6, 2017
Many user reports claim that restarting or even fully restoring the device doesn’t remove the line. The flaw appears to be a hardware defect, and Apple is replacing the affected units without any issue.
Apple declined to comment on the issue.