Please remote into the IoT device to check the settings. Under “Cortana” the “Let Cortana respond to “Hey Cortana”” check to see if it is disabled. Enable that setting “Hey Cortana” and it should work just fine. If you don’t have mouse/keyboard/remote connected in order to go through the setup (language, wifi, Cortana) it will default to “Hey Cortana” being off. On the older AK it seems like that defaulted to ON.
Full Disclosure: I am an employee of Qualcomm Canada, any opinions I may have expressed in this or any other post may not reflect the opinions of my employer.