An IMPROPERLY installed CNG apparatus with WRONG CHOICE OF EQUIPMENT is what ruins a CVT gearbox since wrong install/wrong equipment reduces engine performance a lot resulting in more thrashing of the CVT gearbox.
So if you have a car with a CVT tranny and want to install CNG, then go for a SIS kit for trouble-free operation - otherwise be ready to bear the costs for a replacement gearbox.
Comprende?