The grey waveform means that the deck isn't selected to PC, could it possibly be that your first SX was bumped and the deck select changed? If not then having the unit looked at by a service center is in order. Before make sure you have updated your firmware and then try the same track again and see what the results ar. Below is the service center links.
Please contact a Pioneer DJ authorized service centre in your region to have your hardware inspected and/or repaired.