Right, I’ve discovered the problem, and it’s a weird one! On my set up, I rely quite heavily on LastVoiceCommand (LVC) to trigger certain events. I
also expose dummy switches to Alexa so that she doesn’t say “I can’t find a device called…”.
What seems to have happened is that Amazon have changed the procedure for reporting on the LVC channel. It now seems to only reports commands which are not linked to a switch being triggered. For example saying, “Alexa, volume up”, or “Alexa, play music”, or “Alexa, what’s the weather like today” (and most other sentences) show up under LVM. But if you say, “Alexa, turn the lights on”, it doesn’t! This breaks a lot of rules I’ve created 
Has anyone else noticed the change? As I said above, this occurred overnight and I discovered the problem yesterday morning.