Does anyone here have rabbits that just never learned to use a litter tray?

I've been keeping rabbits for over 10 years and have always managed to toilet train them all. However at the start of the year I rescued 2 lops (both 3 years old and first time owning lops) and they've just never taken to any of the training. They were neglected by their previous owners and were used for breeding (I got them neutered) so I think it's their upbringing that has created this situation.

It is frustrating to feel like I've tried everything and they still won't stick to using one section of their room for the toilet. They go everywhere and I hate it so much because it's constant cleaning of poop and pee!