Why am I seeing multiple SSIDs on an Asus ZenWiFi Mesh system?

I have three Asus ZenWiFi XD6 nodes in my home. They are interconnected by a wired Ethernet backhaul. The central node, acting as the router, has two SSIDs - home and IoT (which is, essentially, supposed to be a guest network with no access to the home network). Only the home SSID is being offered by all three nodes. The IoT SSID is being offered only by the central node. I discovered this when I tried connect a new webcam to the IoT network in my garage, which gets no signal from the central node, but plenty of signal from the remote node I put into the garage. The ASUS Support page says: How

Question by E McCrory on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.