Diagnosis
Bluetooth pairing failure between the phone and the grill's controller module.
How to Fix It
Force close the Char-Griller app. Power the grill completely off at the controller, then back on. On your phone, go to Bluetooth settings and "forget" any previous Char-Griller connections. Open the app again and follow the pairing process with the grill within 3 feet.
If That Didn't Work
The controller's Bluetooth antenna may have a poor connection. This requires checking the internal wiring harness connection to the control board, which involves removing the controller faceplate.
Heads Up
The app is for monitoring only. The grill must be controlled at the physical controller. Do not rely on the app for critical temperature control during a cook.