Documents containing track changes and numbered styles can sometimes contain erratic header margins, in particular the header can be seen to take up the whole page, resulting in some pages containing only one or two lines of text.
Attempts to move the margin up often fail, or simply move the problem to the next page.
The first thing to do is set the vertical alignment of all sections of the document to Top. In some cases this will correct the entire document.
Alternatively, it is necessary to highlight the end paragraph mark for each affected paragraph and reject the formatting change.
It is worth noting that this issue naturally resolves itself when all tracking is accepted.