While a special ShiftNav [Main] theme location is created for the main ShiftNav Instance, this is not the case for secondary instances.
For a secondary ShiftNav Instance, the menu is assigned via the special settings panel for that instance.
You can assign a menu either directly, or via a theme location.
Assigning a menu directly
To assign a specific menu you have created in Appearance > Menus to a ShiftNav instance:
1. Go to Appearance > ShiftNav
2. Click the +{instance_name} tab for your ShiftNav instance
3. Select the menu you wish to display under Display Menu and save the changes.
4. Applying this setting will override the Theme Location setting.
Assigning a menu via a theme location
To assign a menu via a theme location to a ShiftNav instance:
1. Go to Appearance > ShiftNav
2. Click the +{instance_name} tab for your ShiftNav instance
3. Select the theme location you wish to display under Theme Location and save the changes.
4. If you have not already done so, visit Appearance > Menus > Manage Locations and assign a menu to your chosen theme location.
If you set the Display Menu setting, this setting will be ignored.
ShiftNav does not automatically create new Theme Locations for each ShiftNav instance. If you wish to create new theme locations without adding PHP code, you can use the free Menu Swapper plugin