Charging Loss

If you are seeing a discrepancy with the power recorded by your vehicle as being supplied during your charging session, it is most likely to do with 'Charging Loss'. Charging loss occurs as no charging is 100% efficient, some energy is lost to heat (unintentional, like the on board charger heating up) and deliberate - like the EV battery warming itself to optimise charging. Please note that this occurs with anything that has a battery including smart phones, tablets etc. 

Here are a couple of articles which may help explain charging loss in EVs further:

https://go-e.com/en/magazine/ev-charging-losses
https://insideevs.com/features/711659/ev-charger-efficiency-losses/