I can't replicate that since we don't have mac 10.11 to test. (Test labs are current and back 2 for Operating Systems generally, so for a Mac, we have 10.12-10.14)
Call Xerox and report it to see if they can fix it.
When printing jobs with an odd number of pages from MacOS 10.11, with Xerox driver version 4.20.5, the last page is left out. If I print to PDF file, then use the machine's web interface to submit the PDF file, then it prints all pages. So this seems to be a driver bug.