This may happen when one of the radios has a different configuration, this can be solved by resetting both radios to default.
To reset the radios to defaults using Mission Planner:
- Connect the telemetry radio to the computer, select the serial port and 57600 bauds, don’t hit connect yet.
- Go to Initial setup, optional hardware, 3DR Radio.
- Click Reset to Default.
To reset the radios to defaults using APM planner:
- Connect the telemetry radio to the computer, go to initial setup, 3DR Radio.
- Change the link settings selecting the serial port for the telemetry and 57600 bauds.
- Click Restore Defaults.
If you are not able to establish a connection after executing this procedure, try to re-install the firmware of the telemetry radio as is shown previously.