After updating to 8.4 two weeks ago, both cameras stopped working. The camera app shows a black screen and once you press any of the buttons the rest of them stop doing anything. The shutter button 'clicks' but does nothing, then the settings randomly disappear. No other modes work, though I can scroll through them. I can not change to the front camera. Other apps that use the camera will open, but I only get grey screens. (Some crash right away.) I've restarted, updated to 8.4.1, but nothing. Any ideas?