AirPort Express extending connects in the wrong order
I recently encountered the same issue and was able to resolve it by removing the Wifi connection in System Preferences > Network.

Here you can select the Wi-Fi interface from the left panel and click the "-" underneath this panel. Then, add back the Wi-Fi interface by pressing the "+", select Wi-Fi and attempt to connect to your desired network. 

This should then place all devices in the correct order by connecting to the device that creates the wireless network as opposed to those devices that either join or extend it.

Best of luck.