iPhone X External buttons delay.

I have an iPhone X with an intermittently fault. All external buttons (side, volume and mute switch) have a delayed response. The touchscreen is fully responsive, no lag or anything, but whenever I use any external buttons they take 1-2 seconds to respond.

I’ve noticed that it also takes longer than normal to recognise when I disconnect the charger when this happens.

I’ve tried performing a DFU but that didn’t fix it. I’m guessing there’s something wrong with the motherboard, but not sure what exactly is causing this. Any insight would be greatly appreciated.