My rabbits have started fighting, advice please

Hi, I'm new to the forum and looking for some advice with my two bunnies.
I have a male and a female bunny, both neutered. I have had them since they were babies and had to seperate them due to finding out that one was a boy. Got them neutered and rebnded them in June, all went great they were grooming and snuggling with no issues, in July they had a fight and lily ended up with a nasty cut on her eye, we separated them and kept them apart until they had both fully healed. We managed to bond them again and all was going well until I went out to see them after work today and there was fur everywhere! No cuts from what I can see just lots of fur pulling, yet they were happily sitting together, spent a lot of time with them tonight, kept checking on them and when I went to do the final check they had done it again!
I have separated them as I don't want them to hurt each other, we just really don't know what to do now? Do we try and bond them again after a break or would they be better off apart?
Sorry it's so long but could really do with some advice on this.
Thanks

Is there anything that could be setting them off - other rabbits nearby perhaps?
I used to have a bonded pair who were fine but the sight/sound/smell of another rabbit would have them at each other's throats.
Are they both in full health? Sometimes if one bun becomes sick the other will turn on it.

Not that I can think of. We haven't been near any new animals, so no new scents. We have a couple of cats come in the garden but they can't get near as the buns live in the shed.
The only thing I thought could be a possibility is that they haven't been out as much lately due to the rubbish weather. They are now seperated in the hutch, she seems happy but he seems Fed up.

Can they see the cats from the shed?

No, the only time they see one is if they are in the run and one comes in the garden. I don't think it would be the cats I just don't know what it could be, they are best friends one minute then all of a sudden start fighting. This is the second time now I've had to seperate them, the first being about 6 months ago.

Its unusual for neutered male/female pairs to fight. If its possible i wonder if pointing a video camera at them would help you work out the triggger.

It could be something like a cat and one bun is taking out the frustration of not being able to chase it off on the other i.e. referred aggression. Food can be another trigger.

In everyone's past experiences is it worth me bonding them again or is this something that is likely to keep happening?