This topic is rather old, but as I had the same problem just today did a few tests, I thought I might share my findings with you in here.
As above, my Austere Bee didn´t produce any Powdery Comb but Parched Combs in bulk using an Alveary with Frame Housings in a Plains Biome.
After some trial and error testing I mived the exact same Alveary into a nearby Desert Biome and suddenly it made Powdery Combs.
TL: DR Austere Bees seem to only produce Powdery Combs when they are actually located in a Desert Biome.