iPad screen freezes up
My iPad (Air 2, 11.4.1) screen occasionally freezes up but with increasing frequency. It does not respond to any touch actions, pushing the home button, double pushing the home button or holding the turn on/ turnoff button to power off. Once, plugging in my power adapter got it going even though batter had adequate charge. Eventually the spinning gear shows up on a black screen and then the passcode screen come on. Then it is ok until the next time it freezes.
iPad Air Wi-Fi, iOS 11.4.1