I clean flashed 91.1 about 2 weeks ago. I love it. My phone has become a little faster than before and I like the new Sense UI. But for the last 3 days, I am having a weird issue. When I press power, the lock screen doesn't show up. And this happens randomly. I have had to long press the power button (10 secs) to restart the device each time this has happened. It happened thrice yesterday, and already twice today. Is this a known issue? Any fixes or suggestions? Thanks.