Hi! This is actually and old problem but I have alway handled it the hard way, just to redo the page. It seem like you can brake a page created in Cornerstone by misstake edit it with, for example, the WP editor.
The broken page still looks good in the front end but it will not be recognised as a CS page when you try to edit it.
Is there a way to “repair” a page so that CS recognise it again?