Definitely Screen burn.
I inherited my wife's Verizon Note 4 a few months ago when she got a new phone. It had similar screen burn at the notification bar as well as a few of the home screen icons could be seen. Didn't affect the function, but drove me nuts. I really loved the phone other than the screen burn. I was just getting to the point that I couldn't take it anymore and was considering getting another phone.
I a WTH moment one day and stopped by my local Verizon store, told them my screen was shorting out and showed the guy the screen burn. I knew from online research that typically screen burn isn't covered, but I didn't tell them that. The guy at the store looked at it, pulled the battery, restarted, flipped around a few screens and apps, and then said it was definitely broken.
I got a replacement Note 4 (refurbished) delivered the next day. Perfect screen and has run perfectly. I was surprised how well it worked out.
T