You may want to call your county extension agent to see if they have some clues. I have hellebores in shade and sun and the soil is clay and they bloom fine. Some of the younger ones don't bloom right away but since you said you have had some for years, that is not the issue.

The folks who run Pine Knot farms, which specializes in hellebores, will be at the Lewis Ginter Botanical Garden plant sale in May so maybe you can connect with them and pose your question to them.

Not an issue I've had. In my experience helleborus x hybridus (orientals), bloom sparsely their first year blooming, then quite profusely thereafter.