Can't cleanse the sanctum of Solace

I’ve already met the Witch of Wisdom, cleansed all 4 sanctums, and killed Antumbra’s Sword and Antumbra’s Staff, but the Witches faction quest is still stuck on Sanctum of Solace.

I can find both puzzle items. One places fine, but Fusion Reactor Core XV will not go into place. When I go near the puzzle area, I get the voice line: ‘A little impatient, aren’t you? You can’t do anything right now.’

Since I already met the Witch of Wisdom and already cleansed all 4 sanctums, I’m wondering if I sequence-broke the quest or bugged the progression.

Does anyone know a fix?