IPhone X has no sound and reboots itself at random

A few weeks ago my iPhone X suddenly lost all sound. When I try to play anything with sound the phone just freeze for a few seconds and the volume bar shows up.

The phone also reboots itself at random, it reboots even when I’m not touching it.

This goes on for days until all problems just dissappear - and then comes back again a few days later.

I have tried doing a full reset and set it up as a new device but it’s not fixing anything.

I’m thinking that it’s a hardware issue but why does it only last a few days?

Could it be a bug in the last iOS update?