Server Information
osTicket Version v1.11 (7b1eee8) — Up to date
Web Server Software Apache/2.4.18 (Ubuntu)
MySQL Version 5.7.25
PHP Version 5.6.40-1+ubuntu16.04.1+deb.sury.org+1

Getting this error when trying to print ticket thread:

PHP Fatal error:  Call to undefined function Mpdf\\Image\\random_int() in /var/www/html/osticket/upload/include/mpdf/vendor/mpdf/mpdf/src/Image/ImageProcessor.php on line 834, referer: http://name.domain.com/scp/tickets.php?id=11
PHP Stack trace:, referer: http://name.domain.com/scp/tickets.php?id=11
[Mon Mar 04 07:57:56.709855 2019] [:error] [pid 20536] [client 10.1.11.46:61435] PHP   1. {main}() /var/www/html/osticket/upload/scp/tickets.php:0, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   2. Ticket->pdfExport() /var/www/html/osticket/upload/scp/tickets.php:497, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   3. Ticket2PDF->__construct() /var/www/html/osticket/upload/include/class.ticket.php:3126, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   4. Ticket2PDF->_print() /var/www/html/osticket/upload/include/class.pdf.php:72, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   5. mPDFWithLocalImages->WriteHtml() /var/www/html/osticket/upload/include/class.pdf.php:95, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   6. call_user_func_array:{/var/www/html/osticket/upload/include/class.pdf.php:47}() /var/www/html/osticket/upload/include/class.pdf.php:47, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   7. Mpdf\\Mpdf->WriteHTML() /var/www/html/osticket/upload/include/class.pdf.php:47, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   8. Mpdf\\Tag->OpenTag() /var/www/html/osticket/upload/include/mpdf/vendor/mpdf/mpdf/src/Mpdf.php:15383, referer: http://name.domain.com/scp/tickets.php?id=11
PHP   9. Mpdf\\Tag\\Img->open() /var/www/html/osticket/upload/include/mpdf/vendor/mpdf/mpdf/src/Tag.php:239, referer: http://name.domain.com/scp/tickets.php?id=11
PHP  10. Mpdf\\Image\\ImageProcessor->getImage() /var/www/html/osticket/upload/include/mpdf/vendor/mpdf/mpdf/src/Tag/Img.php:276, referer: http://name.domain.com/scp/tickets.php?id=11

Am I missing a package or library?