My DDJSX Main volume goes Down by itself then back up again

Hello,

I was in the club using my Pioneer DDJSX and noticed something that happened to me for several different weekends. I know it's the DDJ SX and not my computer or USB connection because I currently DJ with an S9 mixer. 

I would be DJing and all of a sudden the meters and volume would go down, to 0. Meaning, no volume at all. Sometimes I would hit the channel fader up/down and it would respond again and go back up to the original volume I had it set at and other times it wouldn't. Sometimes the volume would go down to nothing for 10 seconds, then go back up again. 

What do you think this issue is?