It's something wrong with the router. I did run into a switch issue long ago but for this discussion I take it this is a plain switch and nothing special and this has never worked.
Ask Asus and Tmobile about firmware updates. If you are using a security suite on your PCs and such, that could be it but this is not told.
I have a modem wired with a Asus cellspot router from t-mobile. I have 3 PC's and one switch hard wired to the router. The devices connected to the switch, the PCs and any wirelessly connected device have failed to connect to the router. I am getting a 169.xxx.xx.x address where dhcp is not assigning a valid IP. I have found a work around where I can get an IP and get online, but if I turn off the device for a day or more, it is losing its IP and I have to reconnect again. Why won't the address stick and how do I fix this?