On my alt Warlock character it seems that something went awry with unlocking The Relic. I suspect that I jumped out of the mission at the time since I had remade the character several times, but now I am not able to do (or re-do) the Witch Queen introductory missions and unlock The Relic. The Throne World and the Enclave can be accessed, but Ikora will not be in the Enclave and the Relic, as well as the thingamabob on the side, show as being Inactive. Furthermore, when looking at the area map under the Savathun's Throne World / Replayable Missions label, there are no icons and thus no quests to replay. Attempting to unlock it by joining a friend on that mission or joining, getting lead and them departing did not change the situation, despite having cleared the mission in both instances. The Lightfall introduction mission did work as expected and everything on my main Hunter is also working as expected.