After months of turning my Philips Hue lights on and off using Siri, I found myself unable to set a scene today. This fixed it for me:
– kill the Hue app on iPhone
– go to settings -> HomeKit
– click Edit and delete the home named “Home”
– start Hue app
– go to “Siri voice control”
At this point the Hue app should ask you to pair your hub again using the iPhone camera.
You won’t lose your HomeKit scenes doing this, but you will lose any timers and triggers. You will also have to re-add your rooms to ‘Home’ and re-create any zones you had. I also had to re-pair an Eve thermostat.