5330dn Mono Laser Printer is printing random pages twice

In my company we have a Dell 5330dn for printing labels on A4 sheets. When we send a file of labels to print, it will randomly print some of the pages twice, though this does not seem to happen in every file we send to print.

I.e.: a label file is at least 50 pages long, and it would print pages 5,6,10,24 and 41 twice. Every other page is single copy.

The labels are printed using Seagull scientific Bartender program. We've been printing labels like this for over six years. And ever since we've replaced our old HP printer with the Dell 5330dn, these incidents started happening. We do not want this to happen, because the labels are used for privacy sensitive documents, and a random number of double labels being present in a batch causes a lot of problems later on.

We've tried to reproduce any user type action that might interrupt the printing process (which we thought might be responsible for these incidents), like not enough paper present in the tray, pulling the paper tray open while printing, even randomly mashing buttons, these incidents cannot seem to be reproduced. The problem maybe related to the printer itself, but we are baffeled as to how.

Anyone got any ideas?