NEXT GEN scanlines YAY! (next gen because retro was horizontal)
TBH seems to be some kind of GPU problem not the game as far as I know. I mean there would be other reports of stuff like this happening in AC if that would be a game bug.
So it seems like it is some kind of design choice that puts load on the GPU and yours seems to have a problem dealing with it. But thats just a guess.
EDIT: If its the console then it already is broken so you should stresstest it try to find a place where those lines appear and stay there if the lines get worse its certainly the hardware. I could not find anything about that for AC on PS4 but lines and artifacts are signs of a damaged GPU. Also try different HDMI inputs and cables sometimes stuff like that is just cable/connection problem.
