Cannot progress from Act 2 Cruel - all my quests have disappeared

Was at the end of Act 2 on the quest to blow the horn in the sandstorm - I have the horn, but all my quests have disappeared (marked complete). Killing the Dreadnought boss triggers nothing.

Also still had the quest to search Traitors Passage but had already killed Balbala and could get to trials waypoint, so this might have been messed up too.

Has anyone had this and resolved it?

void