I agree that it looks very much like black death....the giveaway is in the veins, isn't it fidget? Plus new leaves, in my experience, should be perfect/unblemished. Black spot develops on older leaves.
Chicky, were the flowers affected too? I mean were they black streaked and poor quality?
Are all your plants the same?
I think it IS black death.....
not much support now but I try to keep hostas apart, cannas, dahlias, salvias, hellebores, everything really so that should disease, pests, etc., occur it would be localised.
I would dig up those plants and not plant hellebores there again
Perhaps others have a different view?