After speaking with a GM, they suggested that I submit an in game bug report (which I did), and make a thread here:
As I understand it, the Artifact Knowledge mechanic is supposed to reduce the amount of azerite needed to level your HoA. This reduction is supposed to occur each weekly reset. However, this has not occurred on my warrior for 4+ weeks. My gut feeling is that it has something to do with my HoA level being relatively high (currently 94, and ~75% to 95), though I have no evidence to back that up.
I tried not leveling my HoA for an entire week (no effect)
I tried keeping my HoA level progress under 50% when the reset occurs (no effect)
I tried running with 0 addons just to ensure it wasn’t a visual bug (no effect)
The artifact knowledge mechanic is working fine on all of my other characters, just not my warrior.