I tried that and it didn't work. I got both after killing 70 of them, the drop rate is just horrid lol

I've been farming little demons for this "Strongest Armor" quest since I started the game. I've already killed forty of them. is the side quest bugged, ridiculously low drop rate or is my luck just disgusting? is there some sort of story barrier I've yet to pass that won't let them drop it?