We have 2 devices already discovered in Alexa. We added 1 more device through our app (3rd party app), then asked Alexa to 'discover my appliances'. Our lamda was called (Alexa.Discovery), and all devices' info (including new one) were returned.
But Alexa responded "I couldn't find any new smart home devices". Tried with Echo Dot, Alexa app, and Alexa web.