If the Favorites tab doesn't include all of your favorited documents, pages, or folders, there are likely two things that could be the reason for it. Please check if one of the two following alternatives apply:
A. Are the files actually still marked as a Favorite?
You will see a red star in the corner of the document/folder or a bookmark on the toolbar in the open document.
B. Is the filter activated?
In the Favorites tab, swipe down with your finger to reveal the controls. In the upper left corner, you'll see the Filter icon. Tap on it and check if a filter applies.