I just defeated Archon as part of step 2 of the Explore Kepler: Fabled quest. Shortly after that I received notification that I had completed this quest. I then returned to Caldera and was then able to redeem Agape from the Altar of Relativity. The bug here is that the Mythic Missions Triumph is not registering the completion of Explore Kepler: Fabled. As a result, I am unable to redeem the banner. I have also spent time seeing if there were any solutions to fix this problem but couldn't find anything. Tried restarting the game a few times and logging in but the quest is still not marked as completed under Mythic Missions.