Skull fort keys??

Recently my friend and I completed a skull fort and we kill 2 pirate captains an ashen guardian and a mutinerious henchman/pirate lord. We received 3 villainous skulls, a stronghold skull and pirate orders quest. We did not receive a skull fort key. We were at crows nest fortress. We sub up a CRATE and an ashen chest and unlocked it with an ashen key. We spent some time searching for the skull fort keys but it was not there. We had killed the captains in a concentrated area so it was not far. Any idea why we did not receive a skull fort key?