Arrow mission not connected but removes you from area and it's easy to end up not meeting the Messenger.
Now I knew where Vivienne Mission started and Dragon Age Wiki's first LIne
"Vivienne is an Orlesian Mage and personal enchanter and adviser to Empress Celene."
So naturally I expected to Meet her in Val Royeaux. Dragon Age Wiki's states
"Wicked Eyes and Wicked Hearts is a main quest in Dragon Age: Inquisition in Orlais, involving the assassination plot of Empress Celene I"
Combined, with the fact that, travel to Val Royeaux is unavailable through the War Map.
Leading me to the obvious conclusion that, I will meet Vivienne during Wicked Eyes and Wicked Hearts.
So imagine my surprise when the Val Royeaux Mage is Morganna and she isn't on my Team either.
Further investigation, led to my discovery that, on pressing World Map, when not at the War Table. Then pressing View on any World Location, unavailable in War Map Mode, actually brings up the Local Map.
Allowing Travel, where and when, the War Table will not.
So I goes straight to Val Royeaux, where the Messenger gives me the Invatation. That's all though. no new World Location appears on my map. The quest is completely broken.
Further checking finds it's actually, Wicked Eyes and Wicked Hearts, that causes the break, before starting this Main Quest, the World Location appears as intended and after Wicked Eyes and Wicked Hearts it becomes unavailable.
Sure, it's a specific sequence that leads to it, but not an unlikely sequence.
Unlikely or not, it's a naturally created flow of events, that is leading a few of us to it.
It's easily avoided by forcing the Messenger meeting to occur, before any arrows are shot by Sara.