My phone did the same thing. I have tried everything. I lost a lot of progress of my applications etc while re-installed my phone many times. I also called the sony helpdesk. They couldn't help. Finally, I called for Sony Care service, because I have warranty. They said 5-10 working day and I get my phone back. This was 3 weeks ago. I think, they neither know, what causes the problem and which is the appropiate solution. They didn't offer telephone exchange, that was our luck, that my husband has an old smartphone and now I can use an other phone while my device is under service. I love my z3 but I think, that I never buy sony again.
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