Might you mean Helleborus foetidus 'Wester Flisk'? Odd that it should have bloomed in summer - it IS a very early flowering hellebore (at least in zone 8), but summer is pushing it a bit. Did you remove the old flowering stems after they finished blooming? That can affect how well it blooms the following season. Also, IME, any foetidus is not a very long lived plant.

I don't care for the nigers so I haven't grown 'Ras Buis' - personally, I don't feel any of them are as gardenworthy as some of the other hellebore species or hybrids. I've yet to see any form of niger that made me salivate.

Sorry posted this in the wrong chain initially.

Like I've said elsewhere, if you grow foetidus in situ from seedlings, you will get a much longer lived plant, usually I remove mine after about 10 years as they get a bit straggly and untidy round the base, but they're by no means dead. I suspect the above were pot grown, transplanted and suffered premature old age as a result.
I agree that Niger is problemmatic, but your 'Ivory Prince' is a selected Nigercors(Niger x Argutifolius) and most of the Niger hybrids form some of the most spectacular garden plants.

Niger still looks very good in a very shelered garden spot, the crystal white 3" flowers in January stand out like a beacon.

Cheers Greenmanplants