I farm all of lower zigazag for the mote of severity. I make sure to keep my backpack capacity below 120 before all boss battles. I fight Ammit and other bosses that drop the mote but many times, on my characters i dont get any drops. not even gold.
It might be just "pure bad luck" but it could be something else. I've noticed recently that I've had several occasions where I've had several battles in a row with no drops and no XP. Most recently this happened while farming the Loremaster who ALWAYS drops something, even if it's only a TC and a little XP and gold. After the third time I happened to hit the chat button and noticed that the messages were there that I had in fact received drops, gold and XP but the icons just weren't showing up on the left side of the screen like they normally do. I exited the game and logged back on and everything went back to normal. Whether it's a coincidence or not I don't recall this situation happening prior to the most recent update.