diff --git a/src-python/models/osc/osc.py b/src-python/models/osc/osc.py
index ef4e1152..a47f1f8d 100644
--- a/src-python/models/osc/osc.py
+++ b/src-python/models/osc/osc.py
@@ -90,8 +90,10 @@ class OSCHandler:
             # エラー発生時にbrowserをリセットして次回再初期化
             if self.browser is not None:
                 try:
-                    self.browser.zc.close()
-                    self.browser.browser.cancel()
+                    if hasattr(self.browser, 'zc') and self.browser.zc is not None:
+                        self.browser.zc.close()
+                    if hasattr(self.browser, 'browser') and self.browser.browser is not None:
+                        self.browser.browser.cancel()
                 except Exception:
                     pass
                 self.browser = None
@@ -140,8 +142,10 @@ class OSCHandler:
         # browserがある場合はクリーンアップ
         if self.browser is not None:
             try:
-                self.browser.zc.close()
-                self.browser.browser.cancel()
+                if hasattr(self.browser, 'zc') and self.browser.zc is not None:
+                    self.browser.zc.close()
+                if hasattr(self.browser, 'browser') and self.browser.browser is not None:
+                    self.browser.browser.cancel()
             except Exception:
                 pass
             self.browser = None
diff --git a/src-python/models/websocket/websocket_server.py b/src-python/models/websocket/websocket_server.py
index 34762e55..299e7032 100644
--- a/src-python/models/websocket/websocket_server.py
+++ b/src-python/models/websocket/websocket_server.py
@@ -138,7 +138,8 @@ class WebSocketServer:
         finally:
             # 停止指示が出たらすべての接続を閉じ、イベントループを終了
             self._loop.run_until_complete(self._shutdown())
-            self._loop.close()
+            if self._loop is not None:
+                self._loop.close()
 
     async def _shutdown(self):
         """
diff --git a/src-python/utils.py b/src-python/utils.py
index 7bc0997b..2676d591 100644
--- a/src-python/utils.py
+++ b/src-python/utils.py
@@ -115,9 +115,24 @@ def printResponse(status:int, endpoint:str, result:Any=None) -> None:
         "endpoint": endpoint,
         "result": result,
     }
-    process_logger.info(response)
-    response = json.dumps(response)
-    print(response, flush=True)
+    process_logger.info(response)  # Log the unserialized response
+
+    try:
+        serialized_response = json.dumps(response)
+    except OSError as e:
+        errorLogging()  # Log the full traceback of the OSError
+        process_logger.error(f"Problematic response object before json.dumps: {response}")
+        process_logger.error(f"OSError during json.dumps: {e}")
+        # Optionally, print a generic error JSON to stdout if needed, or re-raise
+        # For now, we'll print a simple error message to stdout as a fallback
+        error_json = json.dumps({
+            "status": 500,
+            "endpoint": endpoint,
+            "result": {"error": "Failed to serialize response due to OSError", "details": str(e)}
+        })
+        print(error_json, flush=True)
+    else:
+        print(serialized_response, flush=True)
 
 error_logger = None
 def errorLogging() -> None: