I have several sub-menus that appear under specific circumstances.
I have a Main Menu, selected appropriately and appearing correctly on the Appearences, Menu page. The Secondary Menu is also selected.
But on the right hand side only the Main Menu is there, and all of the other menus have disappeared too. Yet if I go to the front end, those menus appear appropriately...!
In other words, the menus have only disappeared in the back end.
I have deactivated all plugins, but the problem is still there.
What could be wrong?