A few weeks ago I got a stuck plug on a GreenLots DC charger that I've used many times. I noticed the handle had a crack on it but I used it anyway (it's a free 50W charger). When the charge session ended I could not get the plug out. I tried to restart the charger for a few minutes (raised 80% to 90%), tried lock and unlocking the doors and finally pulled the yellow cable release, all without getting the plug to release. I never got through to Audi, so. I called Greenlots and they told me to hit the safety-off switch, which is holding the stop button in for 30 seconds.
This worked and the plug finally released, I've stopped at at least 10 different DC chargers over the last year and all have been mostly trouble-free (some EA chargers are slow to start and I've had to try a different charger once or twice), so I"ll write this off as a charger error and not an etron problem.
One last thing to mention - if you ever pull that emergency yellow cable - make sure you put the ring back on the tab. I left the cord out and once the charger released the plug the emergency release cable got sucked down into the fender. Lucky I got the service campaign notice the next day so I was able to get the cable fished out while they serviced the charge level indicator.