Hot glue, loud clickAre you certain that the 2.4GHz antennas leads in the RC are firmly in place on the connectors. Did they go on with an audible click? Did you secure them with silicone or a glue gun?
Inside the controller, make sure you firmly push down the 2.4GHz Wi-Fi module (the one with two U.FL connectors), so it is sitting firmly on the main board and making good contact with the connector underneath. This module is only secured by a small strip of double-side form tape to the main board.
No WiFi icon or WiFi icon has been greyed out?