There could be a few possibilities:
1. If he isn’t neutered yet, it could be that his hormones kicked in. Hormones can cause a bunny to lose their litter habits, even if it’s just a single bunny. If it’s caused by hormones, neutering would improve the situation.
2. I don’t think bunnies “pee when they’re asleep”, as far as I know. In normal circumstances a litter trained bunny would go to the box and pee there before going back into a resting position. Unless they have something like a UTI (Urinary Tract Infection) going on and can’t control their pee. Which brings me to the next point…
3. Is the vet rabbit savvy? The vet needs to be one who specialises in rabbits/exotic animals. If the bunny is getting pee all over his private area and his back paws constantly, it doesn’t sound very normal and could indicate an infection or some other underlying cause. Did your vet run any tests?
4. The litter habits could be getting worse because of Harry’s addition. If both aren’t neutered yet, it’s unlikely that they will bond properly due to hormones. They must both be neutered and go through a proper bonding process (see BONDING forum for more info) to be able to live together. Until then they will both be leaving territorial poop and pee everywhere. They have to be separated completely (not even next to each other, as bunnies can pull out fur through cage bars) to avoid fights. You didn’t mention how old Harry is, but if it’s only 2 or 3 months old then it’s still a baby and baby bunnies will get along with anyone…until the hormones come.
Also, baby bunnies can be hard to sex so you may actually have a male x female combination. This is also a reason why they should be separated until they are neutered/spayed or you may end up with an unwanted litter of more babies.