yilinlesley opened a new issue, #35630: URL: https://github.com/apache/airflow/issues/35630
### Apache Airflow version Other Airflow 2 version (please specify below) ### What happened This happened while I was testing the customized timetable. When I tried to click on the DAG in Airflow UI, it jumped straight to this error page below:  Complete error message is as below: `Something bad has happened. Airflow is used by many users, and it is very likely that others had similar problems and you can easily find a solution to your problem. Consider following these steps: * gather the relevant information (detailed logs with errors, reproduction steps, details of your deployment) * find similar issues using: * [GitHub Discussions](https://github.com/apache/airflow/discussions) * [GitHub Issues](https://github.com/apache/airflow/issues) * [Stack Overflow](https://stackoverflow.com/questions/tagged/airflow) * the usual search engine you use on a daily basis * if you run Airflow on a Managed Service, consider opening an issue using the service support channels * if you tried and have difficulty with diagnosing and fixing the problem yourself, consider creating a [bug report](https://github.com/apache/airflow/issues/new/choose). Make sure however, to include all relevant details and results of your investigation so far. Python version: 3.9.7 Airflow version: 2.7.1 Node: airflowtest ------------------------------------------------------------------------------- Traceback (most recent call last): File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 2529, in wsgi_app response = self.full_dispatch_request() File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 1825, in full_dispatch_request rv = self.handle_user_exception(e) File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 1823, in full_dispatch_request rv = self.dispatch_request() File "/home/airflow/.local/lib/python3.9/site-packages/flask/app.py", line 1799, in dispatch_request return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/www/auth.py", line 53, in decorated return func(*args, **kwargs) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/www/decorators.py", line 168, in view_func return f(*args, **kwargs) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/www/decorators.py", line 127, in wrapper return f(*args, **kwargs) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/utils/session.py", line 77, in wrapper return func(*args, session=session, **kwargs) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/www/views.py", line 2919, in grid dag = get_airflow_app().dag_bag.get_dag(dag_id, session=session) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/utils/session.py", line 74, in wrapper return func(*args, **kwargs) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/models/dagbag.py", line 190, in get_dag self._add_dag_from_db(dag_id=dag_id, session=session) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/models/dagbag.py", line 272, in _add_dag_from_db dag = row.dag File "/home/airflow/.local/lib/python3.9/site-packages/airflow/models/serialized_dag.py", line 221, in dag return SerializedDAG.from_dict(data) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/serialization/serialized_objects.py", line 1406, in from_dict return cls.deserialize_dag(serialized_obj["dag"]) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/serialization/serialized_objects.py", line 1342, in deserialize_dag v = _decode_timetable(v) File "/home/airflow/.local/lib/python3.9/site-packages/airflow/serialization/serialized_objects.py", line 210, in _decode_timetable raise _TimetableNotRegistered(importable_string) airflow.serialization.serialized_objects._TimetableNotRegistered: Timetable class 'uneven_intervals_timetable.UnevenIntervalsTimetable' is not registered or you have a top level database access that disrupted the session. Please check the airflow best practices documentation.` Everything else is fine. Without clicking on the DAG, the timetable is functioning normally with showing the RUN_AFTER & run on the scheduled time. This error page only shows up when I try to click into the DAG. ### What you think should happen instead _No response_ ### How to reproduce I was testing the unevenintervals timetable whose source code is listed here: **https://github.com/astronomer/airflow-scheduling-tutorial** And here is my DAG: `from airflow import DAG from uneven_intervals_timetable import UnevenIntervalsTimetable from airflow.timetables.events import EventsTimetable from airflow.operators.python import PythonOperator from datetime import datetime, timedelta # from dateutil.relativedelta import relativedelta from airflow.operators.empty import EmptyOperator import pendulum from airflow import plugins_manager plugins_manager.initialize_timetables_plugins() default_args = { "owner": "someone", "email": ["[email protected]"], "email_on_failure": True, "email_on_retry": True, "retries": 1, "retry_delay": timedelta(minutes=1), } with DAG( dag_id="test_uneven_intervals_timetable_dag", default_args=default_args, description="DAG to test timetables3", start_date=datetime(2023, 11, 6), timetable=UnevenIntervalsTimetable(), catchup=False, tags=["timetable"], params={"key": "", "email": "[email protected]"}, ) as dag: start_test = EmptyOperator(task_id="start_test") python_task = PythonOperator( task_id="python_task", python_callable=lambda: print(plugins_manager.timetable_classes), ) start_test >> python_task` ### Operating System CentOS Linux ### Versions of Apache Airflow Providers _No response_ ### Deployment Other ### Deployment details _No response_ ### Anything else _No response_ ### Are you willing to submit PR? - [ ] Yes I am willing to submit a PR! ### Code of Conduct - [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md) -- This is an automated message from the Apache Git Service. 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