Pages Out of Order on Emailed Invoices/Bills

I just upgraded to Timeslips 2017 from 2013 and pages on some of the bills that I email to clients are out of order - such as, page 3 will show up as page 1 and page 1 will show up on page 3 of the pdf. This happens on only some client bills, not all. Does anyone know if this is a program issue/bug?