I'm testing the upgrade of printer drivers from 4.22.2 to 5.4.2, Mojave 10.14.6.
I run the driver installer, and after all the drivers are installed to /Library/Printers/PPDs/Contents/Resources/ the installer looks at my installed printers and updates their drivers, this updated driver is located at /private/etc/cups/ppd/.
However only the first printer (alphabetically) of each type is being updated - the rest still have the old driver.
Please see screenshot.
Driver is located here.
You would need to call Xerox and issue a ticket against one of the devices to get the engineers to look at it.
I tried it here in the test lab and couldn't replicate it at all, but that's 10.15, because we simply don't bother maintaining a 10.14 here. But the Engineering team probably would.
It would also take quite some time to test since they would have to completely wipe a Mac then install the 4.2 driver then update to current.
So make sure when you call that you can provide a configuration report for the printer you call in on (it isn't needed to test, but because of process, you simply can't escalate to them without the config sheet)
An email to send the config sheet written to explain in detail what your findings are would speed things along nicely as well.