MR60 No Internet after SSID Change

What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 

Has a power off for 1 minute then back ON with the ISP modem and router been performed since last update?
Be sure to restart your network in this sequence:
Turn off and unplug modem.
Turn off router and computers.
Plug in and turn on modem. Wait 2 minutes for it to connect.
Turn on the router and wait 2 minutes for it to connect.
Turn on computers and rest of network.

Has a factory reset and setup from scratch been performed since last FW update? A complete pull of the power adapters for a period of time after the factory reset then walk thru the setup wizard and setup from scratch. Recommend setting the default DHCP IP address pool range to the following after applying and a factory reset: 192.168.#.100 to 192.168.#.200.
 I would power OFF the ISP modem for 1 minute. Factory reset the router and power it off. Power ON the ISP modem and let it sync. Then power ON the router and walk thru the setup wizard again using a wired PC and a web browser.
Press the back reset button for 15 seconds then release. 

Last resort you should manually download the MS and MR FW files and re-load the MS first and MR lastly using a wired PC and web browser.