You could try moving the potty
. Our 8 month old Syrian used to do that - nest (and pee) in his litter tray. So I moved the litter tray to the other end of his house. He then had two nests - one in his potty and one at the end where the potty used to be. But as I kept emptying the potty he eventually settled in the main nest. He sometimes puts hoards in his potty but I take the good bits out and put them next to the potty so he’s stopped doing that now. It’s a kind of training really while working round their need for doing things in their own way.
It has taken a while but he now sleeps in his nest and pees in his potty