I have an internal firewall set up in the router as the DMZ.
Seemingly at random the hub switches the ip for the dmz to a different device. Today it was my phone.
Apart from the inconvenience and loss of service this causes this is a huge security hole.
To clarify, the devices have not changed IP only the dmz pointer.
Is the IP address of the device you wish to be in the DMZ outside of the DHCP range of the hub and assigned as a static address on the device itself? It shouldn't matter, but it might be worth making sure that it is.