[2020] How do you get the Throwing Bones Memento from Rune-Carved Bone Fragments?

I've collected 10 Rune-Carved Bone Fragment's from plunder skulls, but when i click on them to combine them to get the memento, nothing happens and i get a message "You must have at least 10 Rune-Carved Bone Fragment's". Anyone know if this is a bug or am i doing something wrong? any help appreciated :)