Bunnies suddenly fighting?

Quick description of bunnies for reference:
Spencer: English/Dutch mix, male, not neutered, usually the dominant in the bond, also has allergies and has to get antihistimines, around 6 months old
Colby: lionhead/Lop mix, male, not neutered, submissive in the bond, around 4 months old
(they were bonded when they were around 18 and 10 weeks old respectively)

Last week we moved the rabbits to my partners' parents' house as we are due to move ourselves and for others viewing the flat we were asked to find somewhere else to place the rabbits until we moved. We introduced them to the new area and everything was fine but today after work I got a call that there was hair (mainly Colby's) all over their area and they were acting really defensive against each other. I've been reading up and it could be a number of things; because of Spencer's illness? Because of the move? Because of their ages?

I would just like some advice/ guidance, if anyone has dealt with it before how to fix it would be greatly appreciated!

Because of their gender, being not fixed, hitting puberty. That's what male rabbits do, imho more often than not. A change can be a trigger for fighting, but it happens too without.

What they have before puberty is not a bond. They are kids, but when hormones kick in every other male rabbit becomes a rival, even litter mates.

If you actually want to bond them I would seperate them right now until at least 6 weeks after their neuter, and in the meantime read up on bonding males, you can find quite some stories and advice here, imho that's the more difficult combination, not completly impossible, but it really depends on their characters.
Apart from the risk of injury or death fighting might become learned behavior that they remeber after being neutered - they may have forgotten why, but remember that's the thing you do with that male rabbit.

I can't tell what the chances to bond are, never tried that myself.

Totally agree with Prietler. They are hormonal and doing what rabbits will do at that age. There really is no such thing as a bond before then because it is only temporary until those hormones kick in.

Your timing may have worked out to your benefit. Keep them separated for now and look to have them both neutered. Hopefully by the time they are neutered and have had that 6 weeks post neuter, you will be settled in the new place and you can begin the bonding process there.

Thank you for your feedback, luckily we have the ability to easily seperate them and will be doing so until neutering. Making an appointment with the vet tomorrow to neuter Spencer at the end of the month and then Colby will follow shortly thereafter.