Whenever you lock or unlock an i3, charging will stop and then start. The most likely reason for your problem is that you have delayed charging set in the drive with a departure time. Normally, what happens in this situation is that the charge will start then stop until the off peak period starts (provided the off peak period provides enough charging time/kWhs).
If you set an off-peak period of, say, 2 hours and a departure date of, say, Sunday then the i3 will calculate if there are enough off peak periods to provide the full charge. In these circumstances it will charge for 2 hours tonight; 2 hours tomorrow etc until 100% is reached.
If the above isn't the issue, then you probably have a communications module issue within your charger. Clearly, the way to rule out the i3 is to try a 7kW charge on another charger. If this works OK, then it is a charger issue.