@ToriTutu,

Unfortunately, iPhones have a feature on their phones to Spoof the MAC address of the phone, which will cause the device to be seen as a completely new device in your Deco App. The coming updates to KidShield do allow you to install the app on a phone to help prevent changes to your son's MAC address from tricking the network.

There does tend to be a trend of MAC addresses when they are randomized, so you may see if there are other forums and threads that have been able to relate what types of MAC addresses could be seen from this feature.

I think your best bet is to go through the devices one by one and assign them a name so that you can try to identify the device that you cannot find. You can always quickly block the device to see which device loses connection. 

Otherwise, you will likely want to make use of the overall Wi-Fi scheduling feature to limit the device or depending on the issue at hand, change the SSID/Password, or have him use the IoT/Guest Network which can be quickly toggled on its own