diff --git a/src/main/java/com/catchtable/global/exception/GlobalExceptionHandler.java b/src/main/java/com/catchtable/global/exception/GlobalExceptionHandler.java
index f486311..27bce67 100644
--- a/src/main/java/com/catchtable/global/exception/GlobalExceptionHandler.java
+++ b/src/main/java/com/catchtable/global/exception/GlobalExceptionHandler.java
@@ -1,6 +1,7 @@
 package com.catchtable.global.exception;
 
 import com.catchtable.global.common.ApiResponse;
+import lombok.extern.slf4j.Slf4j;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.MethodArgumentNotValidException;
@@ -11,6 +12,7 @@
 // 엔드포인트의 예외까지 이 advice가 가로채면, ApiResponse(JSON)를 openmetrics 응답으로
 // 직렬화하려다 HttpMessageNotWritableException → 스크랩 500 → 모니터링 DOWN 오표시가 발생.
 // 본인 컨트롤러(com.catchtable.*)로만 적용 범위를 한정해 액추에이터를 건드리지 않게 한다.
+@Slf4j
 @RestControllerAdvice(basePackages = "com.catchtable")
 public class GlobalExceptionHandler {
 
@@ -55,9 +57,11 @@ public ResponseEntity<ApiResponse<Void>> handleSpringOptimisticLock(org.springfr
                 .body(ApiResponse.error(ErrorCode.OPTIMISTIC_LOCK_CONFLICT));
     }
 
-    // 500 - 서버 내부 오류
+    // 500 - 서버 내부 오류 (Unhandled)
+    // log.error 로 클래스/메시지/스택트레이스를 남겨야 원인 추적 가능.
     @ExceptionHandler(Exception.class)
     public ResponseEntity<ApiResponse<Void>> handleException(Exception e) {
+        log.error("Unhandled exception → INTERNAL_ERROR: {}", e.getMessage(), e);
         return ResponseEntity
                 .status(ErrorCode.INTERNAL_ERROR.getHttpStatus())
                 .body(ApiResponse.error(ErrorCode.INTERNAL_ERROR));
diff --git a/src/main/java/com/catchtable/reservation/service/ReservationService.java b/src/main/java/com/catchtable/reservation/service/ReservationService.java
index f32e1f2..736a6a8 100644
--- a/src/main/java/com/catchtable/reservation/service/ReservationService.java
+++ b/src/main/java/com/catchtable/reservation/service/ReservationService.java
@@ -278,8 +278,17 @@ public void cancelReservation(Long reservationId, Long userId) {
             // 결제 미완료: PAYMENT_FAILED로 기록 (사용자 예약 취소 내역과 구분)
             handlePendingFailure(reservation);
         } else {
-            // 결제 완료(CONFIRMED): PortOne 환불 후 CANCELED로 변경
-            paymentService.refundPayment(reservation);
+            // 결제 완료(CONFIRMED): PortOne 환불 후 CANCELED로 변경.
+            // 결제 정보가 없는 비정상 상태(과거 cleanup 흔적 등)에서도 취소가 가능하도록
+            // PAYMENT_NOT_FOUND 는 graceful 처리. PortOne API 자체 실패는 그대로 전파한다.
+            try {
+                paymentService.refundPayment(reservation);
+            } catch (CustomException e) {
+                if (e.getErrorCode() != ErrorCode.PAYMENT_NOT_FOUND) {
+                    throw e;
+                }
+                log.warn("환불 대상 결제 없음 — 취소 진행: reservationId={}", reservationId);
+            }
             restoreInventory(reservation);
             reservation.changeStatus(ReservationStatus.CANCELED);
             eventPublisher.publishEvent(new ReservationCanceledEvent(
@@ -307,6 +316,16 @@ public ReservationUpdateResponseDto updateReservation(Long reservationId, Long u
                 Reservation newReservation = createReservationCore(userId, request.newRemainId(), request.newMember(), request.couponId());
                 newReservation.changeStatus(ReservationStatus.CONFIRMED);
 
+                // payment.reservation_id 에 UNIQUE 제약 — 새 reservation 에 이미 잔존 payment 가 있으면
+                // transferToReservation 시점 flush 에서 UNIQUE 위반. 사전 정리해 idempotent 보장.
+                paymentRepository.findByReservation_Id(newReservation.getId()).ifPresent(stale -> {
+                    if (stale.getStatus() == PaymentStatus.PAID) {
+                        throw new CustomException(ErrorCode.PAYMENT_ALREADY_PAID);
+                    }
+                    paymentRepository.delete(stale);
+                    paymentRepository.flush();
+                });
+
                 if (oldPayment != null) {
                     oldPayment.transferToReservation(newReservation);
                 }
diff --git a/src/main/java/com/catchtable/store/service/StoreService.java b/src/main/java/com/catchtable/store/service/StoreService.java
index 30a82ae..8f13f98 100644
--- a/src/main/java/com/catchtable/store/service/StoreService.java
+++ b/src/main/java/com/catchtable/store/service/StoreService.java
@@ -69,7 +69,9 @@ public List<StoreListResponse> getStores(String name, Category category, Distric
     }
 
     // 인기 매장 — Redis 캐시(TTL 5분) 적용, Cache Stampede 방지
-    @Cacheable(value = "popularStores", key = "#limit", sync = true)
+    // RedisCacheManager는 sync = true 를 일관되게 지원하지 않음 (UnsupportedOperationException 가능).
+    // Cache stampede 방지가 필요하면 Redisson 분산락으로 별도 구현해야 함.
+    @Cacheable(value = "popularStores", key = "#limit")
     @Transactional(readOnly = true)
     public List<StoreListResponse> getPopularStores(int limit) {
         return storeRepository.findPopular(PageRequest.of(0, limit)).stream()