This article applies to RSD0607 (AC750 Dual Band Wi-Fi Range Extender), RSD0608 (AC1200 Dual Band Wi-Fi Range Extender), RSD0617 (AC2100 Wi-Fi Range Extender), RSD0618 (AX1800 Dual Band Wi-Fi Range Extender), and RSD0623 (AC2100 Dual Band Wi-Fi Range Extender).
Check the SSID of your rockspace Range Extender
If your range extender and router use the same SSID (network name), you can only see one SSID in the Wi-Fi network list of your devices.
By default, the extended network of RSD0607, RSD0608, and RSD0618 has _EXT or _5GEXT added to the end of your current network, while that of RSD0617 and RSD0623 use the same SSID as your current network.
If you have changed the SSID of the range extender, it is what you have set.
To change the SSID of your router and range extender, visit how do I change the Wi-Fi name and password on my rockspace routers or how do I change the Wi-Fi name and password on my rockspace range extenders.