probably won't help anyone beyond the point, but:
I wiped out Thalla before getting to the 'speak to the apothecarist' quest.
I realized that after checking the poison flask on the tower, it was spawning a sparrowhawk bowman up the stairs from the apothecarist.
First and second time i reloaded a save i wiped out the bowman, couldn't speak to the apothecarist.
Third time i crouched past him and it let me talk to the apothecarist.