I submitted the following in bug report after going in circles with customer support, but figure this might be better here:
([Season of Discovery] Missing Hyjal's Wisdom / Rune of the Knight)
I do not think this is a bug, because I do remember receiving Hyjal’s Wisdom (why I didn’t learn it then, I have no idea). I think something happened to the item and it is now gone, with no way to restore it.