People who had some "Showtime" app installed had this happen on their Shield TVs. Uninstalling fixed it.

unistall showtime updates

Can confirm disabling showtime app fixes this.

I had the exact same problem with mine, I found that it stopped popping up when I used a VPN

I got the same problem Looking for a solution as well

I had the same problem. I did a complete system reset. I hadnt done it in the jump to 8