My phone is occasionally completely unresponsive. Screen won’t turn on at all. After several minutes, it will reset and come back to life by holding volume and power buttons. Troubleshooting so far has included resetting phone and setting up as new, and exchanging for new phones at the Apple Store twice. It still happens about 2-3 times per week. It will be fine when I’m using it, set it down and it’s dead when I pick it up again. The battery is not the issue. All apps are updated and I’m always on the most recent iOS version (12.3 as of last night). Any ideas how I can troubleshooting further? The Genius Bar folks say it could just be an iOS or phone design bug.