If the Favorites tab doesn't include all of your favorited items (documents, pages, or folders), there are likely two reasons for it:
A. Are the items actually still marked as a Favorite?
For a page, open it and check for the red bookmark on the nav bar:
For a document or folder, check for a red star in the top-right corner of its thumbnail in the library view:
B. Is a Favorites filter active?
In the Favorites tab of the library view, check under the "Favorites" header for the Filter icon. Tap on it and check if a filter applies. For example, if "Documents Only" is selected, you only see favorite documents. Choose "Any" from the Filter list to display every favorited item.