Yeah, it’s really subtle. Here’s a zoom-in of your pic with the brightness and contrast increased:
Ideally, they should all look like the first dark line. That is, one dark line in the middle with equally lighter lines above and below. Skip down 3 scanlines and it’s just 2 mid-gray lines next to each other. Skip down a couple more and we’re back to normal. Rinse/repeat all the way down the screen.
It’s an effect caused by the averaging of the pixels into an uneven integer multiple (that is, 4.5x at 1080p). The remainder comes out as uneven gradients.
EDIT: here’s the same image with the green-tinted lines taken out to make it easier to see the effect: