@GK66
I would assume the router is the issue if you are sure your Roku is connected to "your" network wireless connection and you are seeing the wrong gateway address. (ie. verify you are not connected to another network with a similar/same SSID network name as yours). A bit unlikely with a password requirement, but pranksters will be pranksters.
You can always try changing the gateway address in the router's LAN settings and see if populates correctly in the Roku. (restart both the router and your Roku device after making this change).
Are you seeing a private IP address or a public IP as the gateway (Settings/Network/About).
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102