It is possible for some layers/sublayers to be in Outline mode while others are in Preview mode.
Check the eyeball icon... if it's got a solid iris, it's in Preview mode.. if the iris is vacant, then it's in Outline mode.
Toggling the View Menu for Preview/Outline will not toggle sublayers. Sublayers will stay in the mode they are currently in.
Toggling the View menu item only toggles main layers. It doesn't even toggle objects on a layer. The menu only sees top level layers, that's all.
To toggle individual layers/sublayers between Preview/Outline modes, simply hold the Command/Ctrl key and click the eyeball icon in the Layers Panel.