[JoeReal]

Remember that the range estimate is just that - an estimate. When you unplug it, it recalculates the range again based on the stored kWh and your efficiency history as well as a number of other factors. You're probably just noticing the estimate being off because it was recalculated from scratch right after the battery was plugged in (charging the battery causes a change in temperature and can change the balance of the cells slightly as well).

My range estimate though is accurate. If I don't plug it in and continue driving, I'll get or beat the EV range estimate displayed.

The drop, however, is real in the sense that if the EV range drop is bigger, I'll have to recharge longer. If the drop is smaller, then my recharging time is shorter, that is, after driven it for the same miles but with a higher EV range estimate displayed.

 

[JoeReal]

That doesn't make a whole lot of sense (that's quite a lot of energy to just suddenly disappear), but it could have something to do with what emartin00 mentioned, which is that the charging system probably spends some time at the very beginning of the charge cycle balancing the cells, which could result in a "lower state of charge" as observed by the battery controller. It could also be that some of your cells are misbehaving as has been observed by a number of users on the forum...I would keep an eye out for any DTCs or charging errors, as it may be a sign of a battery about to fail.

Or the possibility that the portable OEM EVSE could be playing some tricks as well.