This is a pretty common issue with label sheets. The most common cause of the issue is that your priter can't print on Letter size stock from top edge to bottom edge. Instead, the printable area is at least a bit smaller than that. If the minimum bottom margin for your pinter is even a tiny fraction samller than the bottom margin of your label form, you can get a page break before the last row of labels on the page instead of after it.
The fix is to "tweak" the layout part sizes on the layout until entering preview mode shows all 10 rows of labels and the labels still align acceptably on the individual labels. In layout mode, you can select a layout part and then use Height box on the inspector's position tab to make very small changes in the height (size) of the layout part.
Thanks! I tried a slightly different but simpler route that, to my amazement, worked. I formatted a custom page size for the printer and made it 11.1 inches long. Now I just have to remember to use it when I print labels. If it is such a common problem maybe the folks who make the software could describe that fix in the online HELP and in the User Guide.