We changed the issue type of an issue from Story to Epic (or, it might have been from Bug to Epic.) . Subsequent to that, we have associated new stories with that epic. However, while the stories in the epic show up in the backlog, the epic does not appear in the epic panel on the left.
I did notice something different about that epic than other epics in the backlog. If you go to the "old" JIRA view of that epic and click on the "..." icon on the top right and select "Agile Board", you get the error message "The issue could not be located on any part of board '*Product Board'. When you do the same thing with other epics in the backlog, it takes you back to the project backlog.
Does anyone have any idea about why the epic doesn't show in the backlog's epic panel?