Word 2016: Borders of table in rotated textbox don't show

I am using Word 2016 (Windows) and I copied a table from Excel into a textbox. Since the table was too wide for portrait orientation (and I didn't want to insert one landscape page using a section break in order to not mess up the footer/header), I rotated the textbox 90 degrees. It looks great in Word. However, once I pdf or print it, the borders of the table vanish. What am I doing wrong? How can I make sure that I see the borders of the table after rotating the textbox? I would appreciate any help!

Thanks!