"Print Layout" displaying strangely in Word 15 for Mac
A bit more Googling turned up an answer: https://support.office.com/en-my/article/My-top-margin-is-missing-993773e9-4be6-44ae-b9ab-7e0a5d2b8298

"point to the top or bottom of a page until the pointer becomes a double-pointed arrow, and then double click."