First memory quest

How do I get the Defeat Harbinger Ganon memory unlocked? I've run through the mission twice now and it's the only locked mission I have still

Edit: Seems to be an issue on apocalyptic where he reaches a certain HP threshold and the game won't count him as defeated since his health bar isn't empty. Going to try the next difficulty down in a bit and report the results

Second edit: Yep, it's a bug with apocalyptic mode. Very hard and lower difficulties work correctly, but apocalyptic won't give you the memory point for finishing the mission