You can turn Wi-Fi off and on again by going to Settings > Wi-Fi and tapping the slider.This has been known to help a couple of people in the thread linked above. Some lose their connection despite being within range of their router, while others have a constant connection but are notified that they’re currently offline.
Like the Bluetooth issue above, Xperia XZ Premium owners have also been losing their Wi-Fi connections. Problem: Constantly losing Wi-Fi connection
Alternatively, you can install the Xperia Companion program for PC, and use it to backup, restore, update, and repair your phone. You can perform a factory reset by going to Settings > Backup & Reset > Factory Data Reset > Reset Phone > Erase Everything.While you have an internet connection, open the camera and go to the C amera’s settings > More > Help > Camera, Front camera, Flash or Camera button, then follow the steps provided on screen. (Can only be done when camera is in Superior auto mode).
You can try adjusting the camera’s focus by going to Settings > More > Touch to adjust > Focus and brightness.