As I see it, even though they got neutered, they are still juvenils and go through changes growing up. There's more that effects behaviour than a few glands, and at certein times of the year that can resurface more or less even when adult.
Does imo mature at a different pace than bucks, so it well can be that they are sorting out their hierachy again. If it's "just" short chases and humping I wouldn't seperate now, but adapt their environment so that they can get away from each other and hide if they feel like, using things like several cardboard boxes taped together with a kind of maze and several exits, shelfs they can jump onto but only fit one rabbit, a second level since they are thinking pretty 2-dimensional (I have a ramp up a cabinet and windowsills, Dotty sometimes retreats behind the curtains), something like a low table they can go under and can't be humped by the other, and so on.
Under those circumstances some marking is not surprising, if mine start to poop where I don't want them to I either block that area off, or put wood blocks (firewood, or those blocks from pallets, bricks or stones would do too) so that they still can navigate through but not squatt comfortably to do their business. Still have such a stumble garden in front of their actual litterbox because sometimes they didn't bother to hop in.
Anyway, imo really helpful is giving them structured space and ways to get out of each others eyes. When they have an argument, and the loser doesn't leave because he cant that can be seen as affront, and make things worse.
Good luck at riding that phase out, andthat it is just a phase.