Not sure if this is our code or not but when using GearVR if you suspend the game by going back to the OS then resume it you only see a black screen. This error was being spammed in my logcat:

W/TimeWarp: eglClientWaitSyncKHR returned EGL_FALSE

This error actually put one of our testers phone into a bad state where he could only see a black screen, even after a soft reboot. He was using an HMD for gear and when he hit the issue he pulled the headset out and it got wedged into this black screen state.