What the hosting software would not let me revise and post previously:
Avery now provides native Pages v7 templates for download in the U.S., but I see they still are using Word .doc templates in the U.K. as is the case with L7651 — which does not appear in the U.S. inventory of downloadable templates.
The L7651 template opens as a two-page section in Pages, with the first page invisible cells, and the second page visible. Attempting to remove either page destroys the label template. Each label is center aligned, and one has to change that to left alignment, and top cell alignment unless the status quo is the goal. That is a disgusting amount of work. Adding to this is that Pages v7.n offers no data from spreadsheet merge capability.
Life is just too short to be wasting time trying to make a Word .doc template behave properly in Pages v7.
This L7651 opens correctly in LibreOffice v6.1.4 as it is a proper Word clone and all you will see is a single label sheet correctly aligned in the document. LibreOffice also offers data merge from a spreadsheet.
Avery's free Design & Print for Mac software gives access to this sheet, with full creative expression and data merge from a spreadsheet too.