The same thing happens to the lore codex item "Makeb's Mysterious Survival, also tied to [staged Weekly] Mass Exodus. Now that the quest has become a normal [weekly], the lore object is no longer granted, although it is a requirement for Loremaster of Makeb, and thus for Galactic Loremaster. So if you don't have it yet, you aren't ever going to get it, unless they rework the quest, which doesn't seem likely