It sounds like either a strand of the belt has seperated or a piece of the clutch pad has come loose or is worn away.
It's an easy deal to open the CVT, and get a better look. You can remove the starter bendix, and run the bike to see what is happening.
I pull the cover off, and remove the bendix. Then reinstall the cover w/ like three bolts. Kick start, and pull the cover back off.
ThaT'S IF YOU CAN'T FIND THE PROBLEM SIMPLY Y TAKING IT APART.