Hello, i recently got a mister and i am having this problem only with NES core that i have noticed.
Is like tearing where ever i am scrolling to. Here in the video you can see the issue at bottom, top and right of the screen. I selected this game cause it is easy to scroll up and down, but it is happening on everygame. If i selecect hide overscan it dissapear at bottom, but still get it at top or right of the screen.
My TV is a Samsung Oled S95b and i am connecting thru HDMI, thank you.
This is a nes problem from the original Hardware.
Mister copy This 1:1 from original Hardware.
That is standard NES jank 
- try enable extra sprites see if that makes it any better, but if its not you have to live with it I'm afraid.
Not just NES, you will find it in later console games too. The Adventures of Little Ralph (PSX) has a tearing line in the top section of the screen. There is even a thread here about it. And yes, tested it on real Hardware+CRT too. It's there.