- Mention user U on page P
- User U receives a notification
- Delete page P
- Restore page P (optional)
- User U receives internal_api_error_BadMethodCallException when trying to view their notification flyout
For example, see https://test.wikipedia.org/wiki/User_talk:Roan_Kattouw_%28WMF%29 , which I deleted and restored. This has broken the alert flyout on testwiki for Catrope and Legoktm.