OK first DON NOT take this the wrong way. I have seen so many people go to a light with a stick shift and then let the car roll back a touch. Then they slip the clutch just enough to keep the car in place tell the light changes. That is so bad on a clutch. I'm not saying you are doing that but people do it. That causes the lots of problems later on. It can even turn the flywheel blue.
I would replace the clutch.
Causes for clutch shutter. In no particular order.
#1 Warn disc
#2 bad or warn pressure plate springs.
#3 release fork arms bent causing miss alignment of the throw out bearing to pressure plate. This in turn causes 1/2 of the plate to grab before the other half.
#4 operator error.
#5 broken mortises springs in the disc.
#6 broken disc separation springs.