Hue emulation works with Alexa but she says, "device is not responding"

the sonoff works as expected, for example when I say, "Alexa, lights on" the lights turn on, but Alexa goes on to say "Lights isn't responding" - I think this is because it takes a while for the 'ON' status to be delivered to the echo and alexa thinks there is a problem?

anyone else had / solved this issue?

Thanks