I dont think its the headphone,mine are sennheiser hd 202 with adapter kit its pretty tight and solid.Do you have one of those 1/8" to 1/4" adapters in between the C12 headphone output and your cans? Those things always go wonky.
Wiggle and/or replug in that thing.
If not the solution there try another set of headphones.
I didCreate a mono track instead of a stereo track.