In order to avoid the unnecessary processing of dozens of hidden links on each page load, Backdrop now defaults to putting menu items defined in hook_menu() into a hidden 'internal' menu. Previously they were added to the 'main-menu' by default.

As a result, menu items that should be shown in the main menu now need to explicitly define this. For example:

$item['menu_name'] = 'main-menu';
Introduced in branch: 
Introduced in version: 
Module developers