Noise or glitches occurring on the unterminated input sub-channel for the 720221 module is normal.
You must install a short-circuit jumper on the input terminal which is not used. The wave becomes GND level and glitches will not appear.
Another method is to set the Burn-Out function to ON through the CH » Temperature Setup menus. If Burn-Out is set to ON and the input sub-channel is unterminated, the DL850 will interpret the status of the TC as disconnected. So the wave becomes HI level over ranged positions.
Please see the attached file for an example screenshot.