This is usually a short circuit in the load cell cable, or an internal problem in the trimmer box. If the input signal from the load cells is shorted to the excitation voltage, then the scale will first read "Heavy Bag", then display the message "ADC 2", meaning the input is out of range for the indicator.
Check that the load cell cable from the indicator to the scale base is in good condition and not cut, crushed, or damaged in any obvious way. If it is then it will need to be replaced. If the problem persists raise a support ticket with us.