Hi, I am starting this thread as my wife and I both have Xperia XZ phones and for the last month or so they have rediculously slow and barely usable unless you reboot every hour or so and we just found the soluton: The issue is with Sony Movie Creator applciation. There is an update to this app now which might fix it but I never use this therefore I have left it disable and not tested the latest release. Disable the app (Settings>Apps>Moive Creator - Disable) Then reboot your phone into safe mode (hold down the 'reboot' button and click OK for safe mode) Then boot back into normal mode. After doing this my wife and I's phones were superfast once again. Hope this helps someone.
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