Same subnet rules out firewall issue. I'm not sire what else it could be, sorry. Is the firmware on the printer up to date?
My Phaser 6510 is connected directly to my router via ethernet. Every device on my network suffers from the printer showing offline after about 24 hours. I have a wide range of devices that suffer this (Macs, Windows, tablets, mobile phones, domain joined work computers, via wired and/or wireless). My point is, I don't feel it's a setting with one of the devices since this happens across the board. We wake or turn on the printer before trying to print. I've tried using both WSD and TCP/IP ports. Turning on and off SNMP. When the printer shows offline in the Devices/Printers window, I can still ping the printer and also log into the Xerox web GUI via the static IP of the printer. Maybe it's a setting in my Netgear router or in the printer?