I'm using Code Owners to define ownership rules and automatically assign issues. However, even though there was a matching Code Owners rule and the stack trace contained the correct path, the issue was not assigned to the owner.

The Code Owners functionality in Sentry only applies to in-app frames. If an issue contains no in-app frames, Code Owners assignments will not be triggered.

To mark frames as in-app, check if your SDK provides an option to do so, such as the in_app_include option in Python. Alternatively, you can use Stack Trace rules in your project settings to specify which frames should be considered in-app.