FootNote fixes?
As I was adding new footnotes, and deleting old ones, the new footnotes were sometimes on the wrong page (e.g. the page before the footnote reference), and the numbers weren't right - either they were out of sequence, or some numbers in the sequence were missing.

It turned out that it was because I had tracked changes enabled. It seems that MS Word takes account of the deleted footnotes in its numbering and placement of the footnotes.

HOWEVER, If Track Changes is NOT on, the most reliable fix is this: (all versions of Word)
To keep a footnote on the same page as its reference, the only workaround that has been found to be always reliable is to format the line spacing of the body text paragraphs (not the footnotes themselves) to an Exact amount (in the Paragraph dialog).

• Select the paragraph, or the Style, and edit the Paragraph formatting. On the Spacing area change it to Exactly and choose the pt.
• 12 pt is Single spacing, and 26-28 pt is double-spacing. 
• It also helps if on the Line and Page Break Tab you take OFF the Widow/Orphan control.