Is there any plan region in that area? Also is the wall placed in different phase, design option or wrong workset?
I have checked all those, none of them is the reason. Very interesting thing is, I have an area plan of this level, and that wall is shown there; I did tests by applying the view template of the floor plan to the area plan, the wall is still there; I copied the plan region nearby from the floor plan to the area plan, nothing changed. Not sure what caused the difference.
Share the file of that wall area.