One of our customers experienced an issue with GPS while using their new Xperia XZ Premium.
The solution was:
Go into to the service menu, press *#*#7378423#*#* in the phone dialer. Go to service tests > GPS > purge assistance data. Restart phone and try again. Normally it takes a while for the GPS to find your position after you have purge assistance data so have a little patience when you try again. Af
After completing these steps, customer did not experience further issues.