I got my iPhone 7 Plus about 3 weeks ago and it's been great other than one issue. The screen intermittently becomes unresponsive completely and will be like that for about 15 seconds. It then returns to normal for a few more days and then does the same again. I've re-installed iOS from scratch on iTunes, done a reboot holding volume and lock key. It's quite annoying and I'm wondering if anyone else has had the same issue?