I recently got the above named TV, and I noticed that when it is transitioning to a device input, or when when I start a video game (i.e., I'm on the Xbox dashboard already and select a game), as well as while I'm idling on YouTube (i.e., sitting on a video thumbnail) the screen will go completely black (like powered off black) for about a second or 2. Not sure what's causing this. All plugs seem to be secure. I haven't noticed it while playing a game itself, and it didn't do it in the middle of a movie I watched from my 4k player.
