Sony’s Xperia Z Ultra is an incredibly nice, although extremely large, device. The obvious selling point on the device is the large and incredibly crisp and detailed display, but some early adopters are reporting problems with their display not properly waking from sleep, or waking from sleep with green bars across the screen. The problem is reportedly not an Android problem, as the OS is running and functioning, and if the power button is pressed enough times it will eventually turn on properly.
The latest firmware for the Ultra has had some effect on fixing the problem for some users, but not everyone. Still, if a firmware update has had some success in fixing the problem, there’s hope that it’s just a software bug and not a hardware problem.
source: Xperia Blog