I recently just purchased the new Chromecast with Google TV. When watching movies like on Netflix or HBO Max every 15 minutes or so the screen will go black for a couple seconds. And also I noticed on my pixel 5 when watching a movie from the Google TV app I have the same issue. I'm starting to think it's the Google TV app that's causing this.
This is happening to me as well on my Vizio P series. About every 15 minutes on every app. Haven't used the google tv app on my phone though.