I had this before and this morning it happened again. If I have to fill some rolls with the same image I usually keep the print data that Qimage + the Z3100 driver make in the spooler and restart the next jobs there avoiding rerasterisation in Qimage and what the driver has to do. Much faster. Two files there, one with only one image and the other with 3 or more, the last speeds things up, the first fills in the rest of the roll at the end. This works perfectly when the system isn't restarted. If I want to print the spooler file the next morning it will print a much smaller one that is also distorted even when Qimage is loaded in the same manner and the driver should be visible to the printer. The length of that odd print page is always 28 cm, could be including the 2x5 mm marges or not. The distortion can be in aspect ratio and it is hard to to tell how much the image(s) shrink, sometimes it seems related to the 28 cm length, sometimes much more.
I think this is related to the ongoing communication between the driver and the printer and not all the information for a job is in the spooler data. So if the printer gets data from yesterday and the driver + application doesn't tell additional information it defaults to something different. It isn't the default page size of the preferred driver settings it takes but something else. With the older Epsons that I have this doesn't happen, they have far less communication going on and all the information seems to be in the spooler file as it will print fine from that source the next day.
This is related to some problems with Qimage not being able to reset print page size in the driver from a recalled job. I guess that the Z3100 driver + printer avoids API for some communication or sends data there that is not easy to understand for other applications.
I'm warned but wonder if this same issue happens when people report odd size differences from time to time.