It sounds like you may need to dial down the gratuitous arp setting in the portserver. This is the PortServer announcement to your network devices like switches and router to update their arp tables.
The default setting is 1 hour which may be why it shows back up after an hour. I would recommend setting it to 30 seconds to see if this keeps the device on your network.
You will need to telnet into the portserver and once at the command prompt type set tcpip garp=30 <enter>. I would also recommend a reboot after the change which you can do using this command “boot a=r” <enter>.