Cannot access Endgame

I cannot access the endgame content.
I defeated the Act 3 boss, returned to town through the portal, spoke to the NPC, and progressed to the point where I woke up at the Atlas Map home.
After that, I switched characters to transfer some items, and when I tried to activate the Waystone, I was told that "the campaign is not yet complete."
I tried defeating the boss again, but the game still doesn't progress.
When I defeated the boss the second time, there weren't even any NPCs in town.