This has been happening ever since Bedrock came out. Every time I get a notification popup, the whole screen goes black. I do not know why. Achievements unlocking, people joining or leaving the party, even pressing the center button to bring up the home menu cause the screen to black out. It has almost gotten me killed on numerous occasions and I have exploded at people in the Xbox Live party to either stay in the party or stay out because every time they pop in and out my screen blacked.