RuntimeError: Working outside of application context when loading instance config after upgrade

The default value of instance_relative_config in Flask is False. In the application factory pattern, this means configuration files are resolved relative to the application root unless the flag is explicitly set to True or instance_path is provided to the factory function.

Likely explanation vs confirmed facts

• Confirmed: Flask's documented behavior sets the constructor default to False. When False, from_pyfile('config.py', silent=False) and similar methods look for config files beside the module or package root, not inside an instance/ subdirectory.
• Likely explanation: After a failed upgrade or downgrade, developers may find that config files expected in instance/ are no longer found, because the factory-created app instance inherits the new default unless the flag or path was explicitly preserved across the version change.

Minimal steps to verify config loading

1. Initialize your factory function and print app.config['INSTANCE_PATH'] to see the resolved instance directory.
2. Attempt a deliberate config load: app.config.from_pyfile('config.py', silent=False) inside an active application context (app.app_context().push()) and observe whether a FileNotFoundError appears.
3. If the error appears only when the flag is not set, explicitly pass instance_relative_config=True or instance_path=... to create_app() and rerun the load test.

To determine whether the default flag behavior is the source of the issue, please verify if instance_path is explicitly set in your factory function.