I suspect you have a problem and this is not a one off. I'm not, however, prepared to say it's the Volt. My guess is that it's the EVSE. Sometimes my EVSE does wonky things. It's intermittent so plugging in another car might get a different result. If you continue to have a problem with the Volt but not the ELR you should take the car to the dealer. Of course they'll plug it in and it will be just fine! (You know this will happen).
On the other hand maybe it was a one-off. Time will tell.
On the other hand maybe it was a one-off. Time will tell.