black shadow on iPhone 8 inital sign in screen

I just unboxed two brand new iPhone 8's from Sprint. Both have a very strange shadow that only shows up on the inital sign in screen. With my phone, being upgraded from my iPhone SE, it went ahead and did everything, and the shadow does not appear on any of the other white or gray screens. The second iPhone will be my husband's first iPhone and I haven't done anything with it, beings it has this black shadow.

Has anyone else experienced this? I have rebooted both phones, to see if it vanishes, it does not. Should I return them to the local Sprint store no matter what, just to be sure it's not defective? I've googled things and tried to search here but I see things about the camera, nothing like this.

Thanks for your help and advice!

Jacki/Mamaroux2