This is just a stab in the dark, but are your litter boxes old? Like really scratched up and well used?

Maybe if you put BOTH of the litter boxes back in their original positions instead of just one and see if that works and take up the paper. If it does, then slowly move the boxes every other day to where you want them to be.

Good luck with this as I can only imagine how frustrating this must be for you guys.