Since you are in the US wonder if you are really talking about true English bluebells, as in Flora's photo or are instead talking about one of the other, more common ones - many grown over here as Spanish bluebells are hybrids between English and Spanish. In my area these are often disliked as they often grow readily, multiply and come up where not wanted. I ordered English bluebells last year from a US bulb specialist, with a catalog written in such a way as to suggest they should know. What came up this year appears so far to be hybrid or perhaps even Spanish. I have not looked at them closely, with an eye toward technical details as the inflorescence structure really looks wrong for English and no fragrance is discernible - at least without getting down and my hands and knees.

Mmmm yes, this is the next stage of my woodland plan - lots of little blue bulbs. I have always liked squills, especially a rather fluffy one called S.litardierei while my eldest son has an impressive collection of numerous muscari....and of course ipheon, chionodoxa et al. Along with omphalodes and the start of my tiny mertensia colonies, in my mind's eye, I see swathes of cerulean blue. Note to self - save seeds of Geranium sylvestris. Ah trilliums. Years ago, these were some of the first things I sowed from seed. Yep, it took years. If only they had lasted as long in my garden. Somewhere along the line, the fact that they require acidic peaty soil failed to penetrate my dimwitted brain.....so my few wake robins dwindled and vanished after less than 3 years (unsurprisingly, in my sandy alkaline soil).

I don't grow the English Bluebells (Scilla Non-scripta/Endymion Non-scripta), but I have countless thousands of Scilla Siberica which produce large drifts of blue as soon as the snow melts. Followed up by drifts of forget-me-nots (Myosotis Sylvatica) in all the garden beds. Truth be told, I couldn't pick one over the other since they've always been here - brought in with loads of topsoil maybe? Neither of them will stay green all season. The scilla in the grass just get mowed down; the ones in the garden beds will get hidden by hostas, lilies of the valley, ferns, the emerging perennials etc. while they're dying down and eventually disappearing. The forget-me-nots are pretty well finished blooming by the 4th. of July here, the parent plant is starting to get pretty ratty and turn black. I pull them up making sure to drop whatever seeds haven't dropped naturally. By the end of summer, I have scads of next year's blooming plants.

A couple of possibilities. First, the plants providing shade in the shade garden. Are they things that leaf out early? Have they grown large enough at this point that they are providing too much shade very early in the year? Second, "Quite a stand".... How dense are they? Try spreading them out more, and see if that might help. I would try moving patches here and there, in different areas of the shade garden, and see if this helps. You may not find out if it works til next year. But you might be able to pinpoint the problem by seeing which patches flower and which don't. Good luck.