2014 Z and Clutch pedal went soft on me ??

[cobra]

I was driving the other day and I felt my clutch pedal had collapsed at least 1-2 inch maybe to the floor. I still could change gears but something weird like I lost pressure or something. It was on and off especially on downshifts.
I checked what I could and didn't see anything wrong. Took the car to the dealer but everything was back to normal when I brought it in. They checked it out, went for test drive but no fault found. It's been a week now and everything is fine. I wonder what happened. It's a Canadian Z and the dealer said they never had somebody reporting this problem yet. They said If it's a clutch cylinder or hydraulic problem the warranty will cover it so I have two other years. I read a lot of Z's in the States had this problem and Nissan doesn't do anything ??