I can only suggest opening up the cvt case, a couple of bolts, size 10,and have a look inside. Lots of black dust = belt probably needs replacing. Move the variator and clutch in various directions, not only rotational, and check if there is a lot of movement.
Now that i have written this, I am leaning toward the clutch pads or mechanism, but I admit, I am guessing.
Sent from my Mi Max using Tapatalk