diff --git a/src/lib/skeletons/SkeletonBuilder.ts b/src/lib/skeletons/SkeletonBuilder.ts
index 01ddb95b..6466782d 100644
--- a/src/lib/skeletons/SkeletonBuilder.ts
+++ b/src/lib/skeletons/SkeletonBuilder.ts
@@ -253,13 +253,12 @@ export default class SkeletonBuilder {
 	}
 
 	private static CorrectBisectorDirection(bisector: LineParametric2d, beginNextVertex: Vertex, endPreviousVertex: Vertex, beginEdge: Edge, endEdge: Edge) {
-		const beginEdge2 = beginNextVertex.PreviousEdge;
-		const endEdge2 = endPreviousVertex.NextEdge;
+		// Use the vertex's actual edges — chain edges can become stale
+		// when previous iterations of MultiSplitEvent modify the LAV
+		const actualBeginEdge = beginNextVertex.PreviousEdge;
+		const actualEndEdge = endPreviousVertex.NextEdge;
 
-		if (beginEdge !== beginEdge2 || endEdge !== endEdge2)
-			throw new Error();
-
-		if (beginEdge.Norm.Dot(endEdge.Norm) < -0.97) {
+		if (actualBeginEdge.Norm.Dot(actualEndEdge.Norm) < -0.97) {
 			const n1 = PrimitiveUtils.FromTo(endPreviousVertex.Point, bisector.A).Normalized();
 			const n2 = PrimitiveUtils.FromTo(bisector.A, beginNextVertex.Point).Normalized();
 			const bisectorPrediction = this.CalcVectorBisector(n1, n2);
@@ -887,7 +886,7 @@ export default class SkeletonBuilder {
 	private static GetEdgeInLav(lav: CircularList<Vertex>, oppositeEdge: Edge): Vertex {
 		for (const node of lav.Iterate())
 			if (oppositeEdge === node.PreviousEdge ||
-				oppositeEdge === node.Previous.Next)
+				oppositeEdge === (node.Previous as Vertex).NextEdge)
 				return node;
 
 		return null;
diff --git a/src/util/skeleton-utils.js b/src/util/skeleton-utils.js
index 17374edd..ae92a224 100644
--- a/src/util/skeleton-utils.js
+++ b/src/util/skeleton-utils.js
@@ -16,6 +16,39 @@ import wallLine from '@/components/floor-plan/modal/wallLineOffset/type/WallLine
  */
 const EPSILON = 0.1
 
+/**
+ * 오목(concave) 폴리곤인지 판별합니다.
+ * cross product의 부호가 혼재하면 오목 폴리곤입니다.
+ */
+const isConcavePolygon = (points) => {
+  if (!points || points.length < 4) return false
+  let positive = 0, negative = 0
+  for (let i = 0; i < points.length; i++) {
+    const prev = points[(i - 1 + points.length) % points.length]
+    const curr = points[i]
+    const next = points[(i + 1) % points.length]
+    const cross = (curr.x - prev.x) * (next.y - curr.y) - (curr.y - prev.y) * (next.x - curr.x)
+    if (cross > 0) positive++
+    else if (cross < 0) negative++
+  }
+  return positive > 0 && negative > 0
+}
+
+/**
+ * 오목 폴리곤에만 미세한 perturbation을 적용하여 동시 이벤트(MultiSplitEvent)를 방지합니다.
+ * 대칭적 변 길이(예: 45.5, 45.5)가 동일 거리의 이벤트를 만들어 LAV 불일치 오류를 유발하므로
+ * 각 꼭짓점에 인덱스 기반 미세 오프셋을 적용하면 이벤트가 개별 SplitEvent로 처리됩니다.
+ * 볼록 폴리곤은 이 문제가 없으므로 원본을 그대로 반환합니다.
+ */
+const perturbPolygonPoints = (points, eps = 1e-4) => {
+  if (!points || points.length < 3) return points
+  if (!isConcavePolygon(points)) return points
+  return points.map((p, i) => ({
+    x: p.x + (i + 1) * eps,
+    y: p.y + (i + 1) * eps
+  }))
+}
+
 export const drawSkeletonRidgeRoof = (roofId, canvas, textMode) => {
 
   // 2. 스켈레톤 생성 및 그리기
@@ -503,11 +536,13 @@ export const skeletonBuilder = (roofId, canvas, textMode) => {
   // changRoofLinePoints를 roof.skeletonPoints에 저장 (roof.points 원본은 유지)
   roof.skeletonPoints = changRoofLinePoints.map(p => ({ x: p.x, y: p.y }))
 
-  const geoJSONPolygon = toGeoJSON(changRoofLinePoints)
+  const perturbedPoints = perturbPolygonPoints(changRoofLinePoints)
+  const geoJSONPolygon = toGeoJSON(perturbedPoints)
 
   try {
     // SkeletonBuilder는 닫히지 않은 폴리곤을 기대하므로 마지막 점 제거
     geoJSONPolygon.pop()
+    console.log('[SkeletonBuilder] geoJSONPolygon:', JSON.stringify(geoJSONPolygon, null, 2))
     const skeleton = SkeletonBuilder.BuildFromGeoJSON([[geoJSONPolygon]])
 
     // 스켈레톤 데이터를 기반으로 내부선 생성