Highlighted walls overlap. One of them may be ignored when Revit finds room boundaries. Use Cut Geometry to embed one wall within the other.

public static FailureDefinitionId WallsOverlap { get; }

Public Shared ReadOnly Property WallsOverlap As FailureDefinitionId
	Get

public:
static property FailureDefinitionId^ WallsOverlap {
	FailureDefinitionId^ get ();
}