Strange behaviour iPhone 6S Plus searching/no service

Hi,


Trying to fix this iPhone 6S Plus searching/no service, posible BB Ko.
But...
If I restore the device it has service, coverage data etc...
Enter the O.S and works well....
If you reboot the phone it got stuck on Searching/no service.
No more takes signal, until you restore, one reboot and bye bye


Any advice on this strange behaviour??

Can anyone point me in right direction??


Thanks!!!