The problem is that your background ended, is still scrolling and the background of the layer is transparent. So the game has nothing to draw there so it just repeats the last pixel available
Yeah but I also tried having the last background section to not move and make it's dt 0, tried to have when player collides with background to have animation stop and so far still nothing works. I just need it to stop scrolling when player reaches that last background section. If not possible then maybe I'll just have to add more sections for the boss battle I guess