I was playing around with frost dk and noticed that my frost strike and obliterates were not working at all, the animation would go off and no error message would appear but the abilities would do no damage. I had a two-handed weapon transmogged as the legion artifact weapon which seems to break these abilities, as when I swapped off of it back to the original weapon, the abilities magically worked again. This is replicaple after testing it with other fellow dks and all of them experienced the same thing.