Did you ever get an answer to this question? I'm having the same problem--adding a second sphere into IoT Central gives the error:
A device with this id already exists in this application
even though it's a new device.
I tried to add second Azure Sphere Device to my tenant, but when I try to run AzureIoT Sample App and I see:
IoTHubDeviceClient_LL_CreateWithAzureSphereDeviceAuthProvisioning returned 'AZURE_SPHERE_PROV_RESULT_PROV_DEVICE_ERROR'.
ERROR: failure to create IoTHub Handle - will retry in 60 seconds.
Of course, when I try to add a device using ID to Azure IoT I receive "A device with this id already exists in this application".
So I think it is just because:
After you complete these steps, any device that is claimed into your Azure Sphere tenant will automatically be accessible to your Azure IoT Central application.
So what to do? How to add this device to IoT Central?