Sound missing in either left or right ear cup

This is a mistake we have seen a few times. It usually comes up if 1 of 2 things happen.
Either the plug connecting the headset with the cable is not fully attached into the headset, meaning only 2 of the 3 poles are getting a signal. This would mean that only one earcup is playing AND it is playing the sound from the opposite speaker e.i, left sound is being played in the right ear cup, and nothing in the left earcup.

Or it could be because the jack connecting the cable with the PC or the controller is not completely attached and needs to be pushed all the way in.