XBox One sound stopped for headphones connected to controller

I was playing a game yesterday and everything was fine.
I paused the game, put the controller down, and left everything as it was.

Today I came back, plugged my simple headphones into the controller, and there was not sound.

I rebooted the box but still no sound.

It turns out my controller has a firmware update ready to install, although there was no indication of that, and after installing sound was back to normal.

You can check and update the controller via the Settings > Devices & Accessories menu (or similar). Find your controller and there will be a tile for updating it.