I have just noticed that when using Spotify via Google Cast on NVIDIA Shield TV my app will disconnect from the TV but will keep playing on the TV. When I reconnect it stops the music and starts from where it disconnected.
I don't know if others have this issue but I think it shouldn't stop the music when you connect again. Should just synchronize with eachother.
Now I know I can use Spotify Connect with the NVIDIA Shield TV app but I don't want to keep changing the account it's signed in to. This is why I use Google Cast instead.