Please note I'm experiencing a similar issue with the Alexa integration since a few days. I'm frequently getting an error message that a device is not responding and finally the change will happen much delayed. This has made my whole system unusable as we heavily rely on voice for light control.
You can test it by noting the time, then trying a device via voice. Then check the event history for the device. You should see a command-on from Alexa, then an "on" event from the device. Compare those times to when you issued the voice command to determine where the delay is happening. If the delay is between the Voice and the command-on then the delay is probably on the Amazon cloud side.
