Looks like one of my nucs bit it, but the other nuc and the two full hives are going strong. It's 50 degrees today, so the hives have been cleaning out dead bees and flying around a bit. This one was conspicuously inactive. Because of the inactivity, I decided to crack it open.
There was still capped drone brood, so I'm guessing it's been dead a while. I poked open one of the cells (a few, actually) with a matchstick, and the pupa didn't come out ropy, but was grey scum. See pics below. It looks like there were some supercedure cells, too. Any opinions? Since there's still honey and pollen on these frames, I'd like to save them for potential use in the future if this isn't some terrible disease.
Dead bees all at the bottom:
The grey pupa (The speck of orange is just the wet wooden end of the matchstick):
One of the 3 center frames:
Outside frame with queen cells:
Thanks for the input!