This whole thing has made Xerox look completely incompetent imo. We'll then have to see if that makes a difference (expected not to) and then we'll likely need to get the machine replaced and hope the new machine doesn't have the same unfixable bug. The engineer's now ordered the parts and will be back in a couple of days to fit them. Xerox HQ require engineers to replace two pieces of hardware in the machine as the recommended step although in this other engineer's experience, that almost never works and the whole machine has to be replaced but it's a hoop HQ basically make them jump through. The engineer spoke to a colleague who has a lot of experience with these machines and he said that they've changed that field to write protected because of Energy Saver stuff and in his experience some machines have this wake on sleep issue, some do not. Unfortunately, this is now a protected field and cannot be changed.
The fix is to enter diagnostic mode and change an NVM value to disable deep sleep, as Gabiene said so the engineer tried to do this. The engineer got here this morning and sure enough, found a known issue in the engineer support documents about this model not waking properly from sleep. After an hour long conversation with the Xerox support web team last week, they decided the best thing was to send an engineer out.