It often prints, and frequently does not print. It may have something to do with if the description was pasted in, or if the invoice was copied from another.
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Not much help there. The only reliable way to get to the heart of a problem is to be able to reproduce it. I'm unable to do that based on the information you've provided.
I tested again, only with Q2016 R8.
I manually created a three line invoice: the description for line 1 came from the Invoice Items List, the description for line 2 was manually keyed by me when creating the invoice, the description for line 3 was pasted from Notepad. After saving the invoice, I printed it: all descriptions printed.
Then I right-clicked the invoice and selected "Add Reminder". This process likely "copies" from the existing invoice to the new Reminder.
Then I selected the new invoice reminder in Bill & Income Reminders, clicked its Enter button, then clicked the Enter Transaction button. I then opened the newly entered invoice in its register (all the original descriptions were present) and printed it: all descriptions printed.
Finally, I used "Copy transaction(s)"/"Paste transaction(s)" to add a new invoice to the register. That invoice had two lines: the description for line 1 was intentionally blank, the description for line two came from the Invoice Items List and was exactly the same in the Pasted invoice as it was in the invoice from which it was Copied. I modified the newly Pasted invoice to have a current date and a unique invoice number. Then I printed the new invoice: the only line item that had a description in the register had that same description in the printed invoice.
Bottom line: I can't reproduce your problem.