My comment is probably not going to help since it's a mystery to me why so many rabbits will just on their own take to litter box training, and some won't.
When I bought my two Flemmish babies at the bunny farm, they were in an outside perhaps 10 foot by 10 foot enclosure..there were shelves /cages for them and the other rabbits to hop up onto and sleep. All the rabbits pee'd and poop'd on the concrete enclosure floor..no litter box training.. The hocks of my two girls were yellow stained from pee on the enclosure floor. We brought them home and placed them in a pen with a litter box in our living room. We initially let them loose in the living room/dining room when we were at home and placed several litter boxes in the living room/dining room. They just automatically took to peeing in their litter boxes! Nothing at all could be said to be litter box training..they just did it naturally (like my previous rabbit also)!!
The above being said, our now fertile girls do have a pee marking issue. We've been through this with our previous Bunny. They want to mark territory. Bunny's pee marking period lasted about 4 to 6 weeks (?), our present Flemmish babies are also showing a decline in pee marking....since they've marked everything! Understand about pee marking..they do not void their entire bladder for pee marking...a marking behavior can only involve one or two tablespoons of pee....so it's not sometimes all that bad. With hardwood floors and leather furniture, we can here can deal with these incidents.
I have experience with 3 bunnies, but once we had our previous Bunny neutered, her marking incidents came to a stop. I'm hoping that will happen with my two Flemmish girls.