Highlighted room separation lines overlap. One of them may be ignored when Revit finds room boundaries. Delete one of the lines.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 26.4.0.0 (26.4.0.0)
Syntax
C#
public static FailureDefinitionId RoomSeparationLinesOverlap { get; }