diff --git a/src/main/java/vip/fubuki/playersync/sync/VanillaSync.java b/src/main/java/vip/fubuki/playersync/sync/VanillaSync.java
index 7782b95..905eaa9 100644
--- a/src/main/java/vip/fubuki/playersync/sync/VanillaSync.java
+++ b/src/main/java/vip/fubuki/playersync/sync/VanillaSync.java
@@ -1003,7 +1003,8 @@ public class VanillaSync {
         if (deadPlayerWhileLogging.remove(player_uuid)) {
             PlayerSync.LOGGER.warn("A dead or dying player was kicked, uuid: {}", player_uuid);
             try {
-                JDBCsetUp.executePreparedUpdate("UPDATE player_data SET online=0 WHERE uuid=?", player_uuid);
+                JDBCsetUp.executePreparedUpdate("UPDATE player_data SET online=0 WHERE uuid=? AND last_server=?",
+                        player_uuid, JdbcConfig.SERVER_ID.get());
             } catch (SQLException e) {
                 PlayerSync.LOGGER.error("Error marking dead player offline: {}", player_uuid, e);
             }
@@ -1015,7 +1016,8 @@ public class VanillaSync {
         if (syncNotCompletedPlayer.remove(player_uuid)) {
             PlayerSync.LOGGER.warn("Player {} logged out with uncompleted sync. Data won't be saved for safety.", player_uuid);
             try {
-                JDBCsetUp.executePreparedUpdate("UPDATE player_data SET online=0 WHERE uuid=?", player_uuid);
+                JDBCsetUp.executePreparedUpdate("UPDATE player_data SET online=0 WHERE uuid=? AND last_server=?",
+                        player_uuid, JdbcConfig.SERVER_ID.get());
             } catch (SQLException e) {
                 PlayerSync.LOGGER.error("Error marking unsynced player offline: {}", player_uuid, e);
             }
diff --git a/src/main/java/vip/fubuki/playersync/sync/addons/ModCompatSync.java b/src/main/java/vip/fubuki/playersync/sync/addons/ModCompatSync.java
index 56298b2..47c5908 100644
--- a/src/main/java/vip/fubuki/playersync/sync/addons/ModCompatSync.java
+++ b/src/main/java/vip/fubuki/playersync/sync/addons/ModCompatSync.java
@@ -487,7 +487,10 @@ public class ModCompatSync {
                     }
                 }
             }
-            return flatMap.isEmpty() ? null : flatMap.toString();
+            // FIX ANTI-DUPLICATION: Return "{}" for empty slots, NOT null.
+            // Null causes writeModSnapshot to SKIP the write, keeping stale data in DB.
+            // "{}" is written to DB, and on restore applyAccessoriesFromData clears slots.
+            return flatMap.toString();
         } catch (Exception e) {
             PlayerSync.LOGGER.error("Error snapshotting Accessories for player {}", player.getUUID(), e);
             return null;
@@ -511,7 +514,10 @@ public class ModCompatSync {
                     flatMap.put(i, VanillaSync.getNbtForStorage(stack));
                 }
             }
-            return flatMap.isEmpty() ? null : flatMap.toString();
+            // FIX ANTI-DUPLICATION: Return "{}" for empty slots, NOT null.
+            // Null causes writeModSnapshot to SKIP the write, keeping stale data in DB.
+            // "{}" is written to DB, and on restore applyCosmeticArmorFromData clears slots.
+            return flatMap.toString();
         } catch (Exception e) {
             PlayerSync.LOGGER.error("Error snapshotting CosmeticArmor for player {}", player.getUUID(), e);
             return null;