Hi again everyone, thanks so much for your replies and ideas. When first bonded we did some stress bonding, and this got them to go from Minnie Nip Mode to grooming. We did the banana trick. So I can go back and try that again, and smoosh them together side by side. As of this morning they are still unhappy – nipping through the bars, Minnie trying to scrabble. She seems to not like him at all. Maybe the bond is broken. Again, I have to put cardboard around the cage to get them to ignore each other. Yesterday I worked all day, so I let Chewy run around in the other room, so he wasn’t stuck in his cage. They’ve both explored this room before and like it. I put Chew back in their own room when I got home so they could eat together and stay together overnight. I really don’t know where this came from, after 2 peaceful months together. I don’t want to shut one of them in their cage so I might have to use the other room again today. At this point I don’t know if they need time apart, or if they will calm down and get over this problem.

I don’t really have a neutral space. Will that be a problem, if they can only have bonding sessions in places they both know? The reason is because my other male rabbit lives in the other spaces, so they will smell like him, and I don’t want that to cause extra problems. So while I do have a spare room, it’s one Chew and Minnie both already know and have spent time in together, not one that’s completely neutral. I guess I could use the bathtub again, it’s been some time since they were in there and hopefully they’ve forgotten (we used it when first trying to bond a trio but it didn’t go well).

As for environment changes…the only thing that has changed is that about 3 days before the fight in my original post, I put a small shoebox filled with timothy hay in the middle of the room. There are piles of hay in their cages – the cages are left open all day and they both hop in and out of each other’s, taking what they like. Neither have shown possession over these areas. Do you think the new hay box, which I just put there as an extra forage option/activity for them, could have caused a rift?

I wish I could go back a few days and get there before they fought, so I could try to diffuse it (and also see what it was all about)! It’s stressful.

They have their own cages from when they were first adopted, and kept separate at home, before and during pre-bonding.. Both cages are still in the room with the doors open. Before this problem they weren’t using them for anything other than hopping in and out, to get hay and water. So the cages are in there and they could go in both if they wanted to, but they weren’t shut inside. They have the whole room. At the moment I have put the cages side by side, so they can see each other, but not touch when feeding them pellets. I thought if I only used one cage, and left one rabbit out in the room, the other one might be upset by that? Can try a different approach if you think two cages is unnecessary here.

I didn’t think the hay box would be the cause, but as it was the only change in their room in recent times, I thought it was worth mentioning. I’ll definitely try disguising a room, thanks for the idea.

Yes, three in total. We have actually had our other male, James, for much longer than the other two. We originally adopted a second rabbit  last year as a companion for him, and then there was a third who also needed a home, and the trio bonding was not successful. We might try again in the future, we will see. Minnie and Chewy showed interest in each other during the trio bonding attempts whereas James didn’t seem to like anybody. So we separated them all for a while and started pre-bonding and bonding again, this time just Minnie and Chew. They live upstairs and James is downstairs, separated by two sets of stairs. In theory James could go upstairs as he’s free-roam but he never has, he mostly stays in a corner of the room he likes best and occasionally hops around the rest of the downstairs. There’s a gate across Minnie and Chew’s door so he couldn’t get access to their room if he did one day go upstairs. They don’t see each other.

James’s smell could be on me if I go between their areas. You’re right, even though he’s not new to the house, his scent could bother them. I think as has been said their bond seems not very cemented and I will need to go back and work better at it this time.