Bunnies are dying

Hi
We have had 7 bunnies for 6 years. They spent the days outside in large enclosed dog kennels.

At night they are brought inside and treated like indoor pets (dogs, cats). In the last three weeks all the rabbits have died suddenly. Even rabbits who our neighbour has.

Does anyone know what might be happening? We have one pet rabbit and one wild rabbit left at this point. I’m
Hoping we can figure out what’s going on

Thanks for any help