Phantom won't drop Phantom Membrane

Hi. So, everytime I kill a Phantom, it won't drop any loot. It only drops exp. I have killed at least 15 phantoms, and, nothing.

This world was made in survival, and has never been in creative mode. Also, it's hard mode if that helps with anything. Every other mob I have come across in this world drops loot btw.

Thanks for hearing me out.