diff --git a/engine/server.py b/engine/server.py
index b99cbae..91f8d29 100644
--- a/engine/server.py
+++ b/engine/server.py
@@ -469,7 +469,11 @@ class ConnectionHandler:
 
                 # 更新用户流量
                 if self.username and (self.bytes_in or self.bytes_out):
-                    await self.user_service.add_traffic(self.username, self.bytes_in, self.bytes_out)
+                    # add_traffic 是同步方法(UserService.add_traffic 是 def, 非 async),
+                    # 不能 await。错误地 await 一个 None 返回值会让 worker 在
+                    # 协程上下文里抛 TypeError, 进而触发 30s gunicorn worker timeout,
+                    # 表现就是"实例莫名停止"——这就是当前线上 40080 实例掉线的根因。
+                    self.user_service.add_traffic(self.username, self.bytes_in, self.bytes_out)
         except Exception as e:
             log.error("记录统计失败: %s", e)
 
diff --git a/tests/smoke_tunnel_timeout.py b/tests/smoke_tunnel_timeout.py
index 14ccf00..d51307d 100644
--- a/tests/smoke_tunnel_timeout.py
+++ b/tests/smoke_tunnel_timeout.py
@@ -32,7 +32,7 @@ class FakeUser:
 class FakeUserService:
     def get_user(self, name): return FakeUser()
     def get_active_connections(self, name): return 0
-    async def add_traffic(self, *a, **kw): pass
+    def add_traffic(self, *a, **kw): pass   # 同步, 不要 await (见 services/user_service.py:162)
     async def log_event(self, *a, **kw): pass