I have 2 male rabbits, we bought them together as babies, they shared a hutch, had them neutered as soon as they were old enough, as recommended by the vet to hopefully stop them fighting. They also ran free in the garden from 8am - 10pm everyday.
All fine for 4 years, seemed to love each other, always cuddled up at bedtime, but one day I looked out of the kitchen window and the garden was covered in fur, chunks everywhere, and the little rabbit chasing the big one round and round, biting chunks out his rear end. Had to use the hose on them in the end, I couldn't separate them.
I'm waffling sorry....long story short, we had to separate them, they live in separate hutches, and can't be out at the same time, so they get half a day each in the garden. They really do not like each other now. We have tried re-bonding them but it ends up in a fight again, and once they start they're so difficult to stop, we've ended up covered in scratches and bitten.
It's always worth trying to re-bond, we tried everything that was recommended to us, but nothing worked I'm afraid. Rabbits are a difficult pet in my opinion, and as much as I love my boys, I would never have any again, they're hard work.
Good luck