Welcome to PokéCommunity! Register now and join one of the best fan communities on the 'net to talk Pokémon and more! We are not affiliated with The Pokémon Company or Nintendo.
Happened to me too, It must be from a different version of photoshop.
What I did though is just select an 8x8 pixel section, and make sure it was a multiple of 8 away from the edges. then i filled in that selection with black on the "Routes Background" layer.
In the end, it doesnt matter how...