Here is something similar reported on Juicebox and Chargepoint very similar to your report.
We would recommend checking to see if GM has any sort of update for the Vehicle, or checking the GM Volt forums to see if anyone has had a similar experience.
The Charging station will not change from Ready to Charging without being commanded from the vehicle.
What can be done to prevent this from happening?
That behavior is very strange. The Vehicle controls the transition from State B (Connected) to State C (Charging) by pulling the voltage down from 9V to 6V.
Kinziulis
Volt 1 gen 2015,
When the car finishes changing