Causes
Low oil.
Wrong oil.
Using the throttle to hold you on an incline. Instead of using the break.
Hauling/towing heavy load in high gear.
These are a few I can think of.
Best way to test a wet clutch or a CVT belt or something else.
Raise the rear of the machine. Remove the cover on CVT housing. Start machine and put in gear. See if the CVT belt is spinning the primary and secondary.
Turn off machine. Leave CVT cover OFF and lower the machine. Now start and put in gear and give a little gas. Does the primary sheave turn but the CVT belt slip? Does the CVT belt slip on the secondary sheave? Does nothing turn?
If nothing turns. Then probably a wet clutch issue.
If CVT belt slips. Then either a belt or junk built up on sheaves. Needed either belt replaced or sheaves cleaned or both,
Hopes this helps and anybody correct me if I'm wrong.