Newly established bonds can be very rocky to variables we can’t even perceive. While the time line isn’t as long as 6 months, I know my local rescue recently bonded two rabbits with each other. It was a seemingly very strong bond, supervised for over a week. When the family came to pick up the bonded bunnies though, one immediately started, non-stop humping the other. We have no idea why– a fragrance a family member was wearing, the rabbit was trying to show off in front of new animals…. but once the family left, the humping immediately stopped and they were completely fine. Rabbit bonds can be very solid, but in those beginning stages, there are things like scent and interactions between them that we aren’t attune to which may upset them or drive the need to reassert dominance.
It could be you’ll never be able to find a reason why, but what’s important is you’ve noticed this new, distressing behavior in the bond, so going back to basics or revisiting some bonding sessions may help the rabbits resolve it between themselves.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.