How can I stop this. Every time I open the app on my NVidia Shield, the last video I was watching automatically starts playing in the background. How can I turn this off? It is almost like you can't stop a stream once you start playing it. I googled it and it was suggested there was a toggle under my user profile, but I don't see it. Any ideas?
It's an option in the settings IIRC.
In any case, you should be using "Smart YouTube TV", not the official app: https://smartyoutubetv.github.io/ . More settings, no ads.
In your main Settings menu for the Shield, go to the Security menu and toggle “Unknown sources” on. Simply download the app with Puffin web browser and use X-plore file manager to browse to the file and install.