diff --git a/docs/RELEASE-NOTES.md b/docs/RELEASE-NOTES.md
index 114ee98..f834229 100644
--- a/docs/RELEASE-NOTES.md
+++ b/docs/RELEASE-NOTES.md
@@ -6,6 +6,7 @@
 
 ### 수정
 - 1h 활성 판정을 parent_name 전체 합산 기준으로 변경 (서브클러스터 분리 후 개별 소수 문제 해결)
+- vessel_store의 _last_bucket 타임존 오류 수정 (tz-naive KST → UTC 잘못 변환 → incremental fetch 0건)
 
 ## [2026-04-01.2]
 
diff --git a/prediction/cache/vessel_store.py b/prediction/cache/vessel_store.py
index b79f031..e73fea4 100644
--- a/prediction/cache/vessel_store.py
+++ b/prediction/cache/vessel_store.py
@@ -114,19 +114,20 @@ class VesselStore:
             self._tracks[str(mmsi)] = group.reset_index(drop=True)
 
         # last_bucket 설정 — incremental fetch 시작점
+        # snpdb time_bucket은 tz-naive KST이므로 UTC 변환하지 않고 그대로 유지
         if 'time_bucket' in df_all.columns and not df_all['time_bucket'].dropna().empty:
             max_bucket = pd.to_datetime(df_all['time_bucket'].dropna()).max()
             if hasattr(max_bucket, 'to_pydatetime'):
                 max_bucket = max_bucket.to_pydatetime()
-            if isinstance(max_bucket, datetime) and max_bucket.tzinfo is None:
-                max_bucket = max_bucket.replace(tzinfo=timezone.utc)
+            if isinstance(max_bucket, datetime) and max_bucket.tzinfo is not None:
+                max_bucket = max_bucket.replace(tzinfo=None)
             self._last_bucket = max_bucket
         elif 'timestamp' in df_all.columns and not df_all['timestamp'].dropna().empty:
             max_ts = pd.to_datetime(df_all['timestamp'].dropna()).max()
             if hasattr(max_ts, 'to_pydatetime'):
                 max_ts = max_ts.to_pydatetime()
-            if isinstance(max_ts, datetime) and max_ts.tzinfo is None:
-                max_ts = max_ts.replace(tzinfo=timezone.utc)
+            if isinstance(max_ts, datetime) and max_ts.tzinfo is not None:
+                max_ts = max_ts.replace(tzinfo=None)
             self._last_bucket = max_ts
 
         vessel_count = len(self._tracks)
@@ -171,8 +172,8 @@ class VesselStore:
 
         if new_buckets:
             latest = max(new_buckets)
-            if isinstance(latest, datetime) and latest.tzinfo is None:
-                latest = latest.replace(tzinfo=timezone.utc)
+            if isinstance(latest, datetime) and latest.tzinfo is not None:
+                latest = latest.replace(tzinfo=None)
             if self._last_bucket is None or latest > self._last_bucket:
                 self._last_bucket = latest