It’s “common knowledge” that Nosema causes Dysentery… but is it actually true?

Yesterday I inspected a group of 40 hives returning from almond pollination. All were strong and healthy, other than two unusual deadouts, which no longer had any bees on the combs, and only a scattering of a few dead workers on the bottom boards. One hive had clear signs of dysentery on the top bars; the other didn't. Upon further inspection, there were small arcs of apparently-healthy sealed brood remaining in both hives, and surprisingly, fresh eggs in the cells below that brood. What could be the cause of these unusual signs?