I just read your other thread and saw you sprayed Nature's Miracle. It may take several treatments and allowing it to thoroughly dry to totally get rid of the smell so they don't keep going back to it.

I agree with catnapper too, maybe something is different about the box or if everything is the same you need to change it or buy a new box. I don't really know, sorry. How frustrating.

One other thought might be Feliway but I don't know if it would help this situation. It is suppose to help calm the cats so if they are stressed for some reason it might help that. I has helped me in the past with Ripley's stress and spraying.