I believe your problem was with your list structuring between your walls and your room elements… The Archi-lab Room.Boundaries node will give you a list of curves and wall elements grouped by your input rooms, so then the vectors will be grouped and evaluated in the Wall.NorthSouthEastWest node by room:
The sublists are for each room; note that there are wall elements (ids) that appear in both North & South because they are in respect to the room.