If Word is set to the bypass, and the driver is set to the bypass, and the print is coming from tray 3, then the driver is not the one to the printers in question.
I have the entire fleet of the Connectkey line, and at least 2 of each model, none do what you are having here.
And that applies to the current native drivers on Xerox.com, as well as any current Global print driver in PS or PCL.
What you are describing, I can only see ever happening in the case of getting new equipment to replace an older model, giving the new equipment the old models IP address, and expecting the prints to go smoothly. Even with a Global driver that isn't the case as the global driver configures itself at install to the device in question, and never again.
If you have any 5955/7855 driver currently available on Xerox.com installed and can replicate this job with the the settings I listed for Word, as well as the settings in the driver, then call Xerox on either model, get to 2nd level, get a log ID and the 2nd level rep will record your process exactly to replicate in the lab, if they can't, they will likely remote into your PC and inspect the configuration or send an analyst on site to troubleshoot.
But since I cannot replicate it, and nobody has ever reported the issue worldwide under the settings and conditions I have put here, there is very little chance it is a Xerox issue. So any onsite analyst would likely not be under contractual coverage.
The only way you could have a fault free print go to the wrong tray when the tray is specified would not be a case where only a particular job would, it would apply to all, and would require your IT dept to go into CWIS > Properties > Login/Permissions/Accounting > User Permissions > User Permission Roles > Edit > Non-Logged in User > Edit and manually disallow printing to tray 5.
The File, the printer and the driver are all probably fine. Word will be the cause due to its defaults.
Go to any troubled user and give this a go:
Open a Word file with a job to be printed on labels. Then select Page Layout > Page Setup > Paper
These settings are found in most MS Office applications and are the bane of my existence as a printer support guy
Applications over-ride the driver always, so these settings matter.
As near as I can figure, the Default tray (Automatically select) which is the default always, actually means to Select the default tray and not as you would assume, automatically select the right tray. That is what Automatically Select is for.
This matches what I would expect of your printer since tray 3 is typically the first of the higher capacity trays, and would be default be the printers default tray.
So send the job after selecting Automatically Select and that will become the new default for that printer within Word and should stay resolved.
If all else fails you can just use this screen to specify tray 5 for that job
Then remember to do the same for every other PC.