Sounds like environmental problems to me, not the right humidity/temp larva die, if they are dead workers don't need to feed them, if they don't need to feed them they don't collect protein, and the whole circle starts again.
Though there is larvae, it just doesn't reach adulthood.
Yep they just sit their in the nest if they are dead, its hard to tell living larvae from dead ones.
But there wouldn't be any larvae if new ones werne't made. :P I see eggs, they turn into larvae, then no cocoon.