After using Android 8 on Sony Xperia xz premium, the volume up&down button did not work. But after restarting my device, it will work and will resume after a short time the volome bottom did not work, Camera shutter button too!(The same situation)
That might be a hardware issue, but to narrow down the issue, boot the phone in >>> safe mode for sometime and see if you experience the same issue, if you do then you could either repair the phone with XC or contact your Local support to get it inspected, if you don't then its a third party app acting up.
