@Kbtcat Here's a description of your router LED status. FW version can be seen from the router WebGUI: Here's how to login your router's WebGUI.

@Gritchu Using the laptop of your mother in law the router WebGUI can be accessed - details. After login they can check the Network Map menu for internet access status, WAN connection type and how...

@rekky Try the following - disable Smart Connect feature here: Connect the laptop to the 5GHz SSID and test again.

@didgeman Have you tried to change the DNSs for your LAN clients in DHCP server menu:

@duckware I think your troubleshooting steps will be of use for TP-Link teams. You can contact your local tech support to report this.

@duckware In what mode your ISP modem works - only modem mode (bridge) or as modem router ? I would suggest when using additional wireless devices to set them in AP mode (Case 1) so you can have only...