Please show us your Page Setup configuration here, Layout and Print Scaling. I print on PDF everyday, everything is fine here
I found this page that makes me think I am not the only one: https://community.tableau.com/ideas/1222
No matter if I print to PDF or open in Preview, when I end up with my PDF the bottom table border is missing. All others are intact.
My bad, I saw your images and thought the problem would be the page headers cut. Is this the only dashboard with problem?
It's a consistent problem across all dashboard and multiple workbooks.