I thought you haven’t saved the changes made in the page which you done after creating the page.So,the data which hasn't saved would have vanished.
When you create a page, its directly added (saved) to the model. When making changes to a page these changes re only saved when you save it (CTRL -S), close it and saved changes or when you run the app and save changes. If the model is closed differently without an active save, changes will be gone.
So answering your question: This can not be resolved other then model it again.
And yes I have encountered this as well, however annoying it happen me 2-3 times in 12 years of using Mx.