I am running Android 5.0 on a LG Sunset. Sometimes, when I am watching some videos on YouTube of browsing the internet, the status/notification bar at the top and the buttons at the bottom just randomly disappear and would not come back until a few seconds later or sometimes even longer. During the time that it does this, I cannot do anything with my phone other than power off and hold the power button for more options. I cannot continue scrolling or typing whatever I want to type. But when I'm watching a video, the video continues playing normally.