For the past week I have been confronted with the connected, no internet dilemma and it's starting to become irritating as I was a frequent user on AndroidTV. After factory reset, changing security options etc. I still am faced with the dreadful message. Although every other device connected to the router is fine, I did attempt to disconnect a few devices from the internet to attempt to solve the problem, though was no help. (assuming that over-connection of the router would be a problem) This made me pose the ISP (TPG) as the problem.
TL;DR - Android TV shows connected, no internet, tried every solution; is ISP or the TV itself at fault?
Have you tried connecting it with wifi or ethernet vice versa with one disconnected. You can also release the leased ip for the device. Also check if the device MAC address is not blocked and see if you can ping the device.