Backing out of my driveway and the brakes went to the floor

On June 2, 2016 I was backing out of my driveway and the brakes went to the floor. The car has 32,393 miles on it at that time. I brought the car to Nissan and the mechanic said adjuster fell into the drum. The paperwork says "right rear adjuster general repairs". It was a $95.00 charge, all for labor, no parts and it was covered under my warranty. On June 21, 2017, exactly one year and three weeks later, my car had 58,770 miles and it happened again. I brought the car to Nissan the paperwork gives no official diagnosis but rather I just need a new brake master