Q:
Hunter's ward
Hm I think that’s just a glitch, have you tried re-equipping the longbow? I believe that did the trick for me when I had the same issue
I think I had similar things happen with the various elite weapons on first equipping, but the moment I used any other attack with the weapon I got the “You have learned X skill” pop up and it unlocked. Like the old old days before NPE when you learned skills by using the weapon and hitting something enough times with unlocked skills would open up the next slot.