What type of litter are you using? I have Okocat litter in my bedroom litter box, and my cats have no issue peeing in there, but if the bedroom door is open, they'll go find a box with silica litter to poop. I've also had fosters that would pee in the box with pine pellets, but then would poop next to the box. Once I switched them to a different type of litter, all poop & pee was in the box again. Unscented, sandy/fine grain litters are usually the most well accepted. I hate clay, but Dr. Elsey's Kitten Attract did the trick for my most challenging cases of litter box avoidance, and then I was able to gradually transition them to a litter I hated less.