Hi, I've just bought a white Sony Xperia Z Ultra and I'm having problems waking up the phone after full shutdown/reset.
The problem happens only after a full reset or a fresh start from complete power-off state. It manifests in a blank screen with just the backlight on and nothing else - this happens after the SONY logo has been displayed as a first screen after booting.
The phone has all the latest updates applied. It takes many tries to get to see the actual booting process (the xperia logo and the color waves animation) - perhaps 10-30 retries and like 30 minutes of trying. .
Eventually, the phone boots up and goes to the desktop where everything is in order.
I've tried recovering the phone back to factory defaults - it went through (using Sony PC Companion). I tried to reset the device and same thing, had to try at least 30 times to go past the blank screen (with backlight on) until I see the boot animation and phone booting up..