The correct way to use CNG on a CVT transmission car is to either use the BRC sequential kit or use a regular kit with an advancer that hooks to the crank and cam angle sensor signals. When you try to advance the ECU with the map sensor - it ruins it.
As the map sensor signal is also used by the transmission internal clutch denoting that the engine is under load and needs power transmitted, while infact you are sitting stationary - this constant correction makes the transmission overheated.
The other factor that heats up the CVT is that it does not understand load other than the MAP and TPS - and is quite preset in the ECU, while driving the pulley sheaves try to bite and the transmission expects that the surge of torque will arrive, which it wont because you are on CNG