Xperia xz premium keeps shutting down

[Aks07]

Xperia xz premium keeps shutting down

[najodleglejszy]

did you make sure that the SIM card slot sits tight in its place? when you remove it, the phone shuts down automatically so perhaps it's not fully inserted.

[Englishmanx]

I used to have the same problem with my former Xperia Z5. It was due to an application that was not installed from Google play . It took me a while to sort it out but after I had gotten rid of it, the phone worked like a charm. 

Advice, never instal anything from outside Google play .