The temperature, weather, humidity, water ect. If it is different while driving and having trouble engaging, which you said was fine, that could be your push rod. If you run your car hard or smoke the clutch or floor it or whatever, that will make it feel different. If there isn't any problem with shifting then you are fine as long as the clutch goes back to feeling normal most of the time. Like I said, driving and weather can easily effect it. Hope that helps because you didn't really explain yourself at all.