SX2 Headphone Mix Volume Low

HELP PLEASE! My headphone mix volume is much lower than my other cues. I did a soundcheck, packed my things up, setup to play for my event again and it wasn't working properly.

I always kept my knob at 12 O'clock so the volume should be the same across. The only way it works is if I blast the headphone volume to max, but then my other line cue's are unusable because it's too loud. Has this happened to anyone? If this a software issue or hardware?