Lately I've been having a problem with my Nexus 7. After a few minutes of being on, it will start to freeze up. Usually when it freezes it eventually unfreezes and go the home screen. After a few minutes from the first freeze it freezes up again, and then goes to a glitched boot animation where the animation is partially off the screen. I then have to force restart it. In short I can use my tablet for 15 minutes and then it freezes. And most often it does that stupid app optimization thing that takes forever. Its super annoying and I really need to find a fix. I'm running Android 5.1 with the latest Dirty Unicorns version (Note: It happened when it had the factory image). Flashing Dirty Unicorns did fix it for a week or so.