Indeed, with GoodCloud enabled, I can unbind the device.
So, I’ve done the following steps:

  • Unbind the device (with GoodCloud activated). The device disappears from GoodCloud dashboard.
  • Deactivate GoodCloud.
  • Reboot.
  • Reactivate GoodCloud.
  • Add the device again in the GoodCloud dashboard.

With all these steps done, I can now access Slate and Flint SSH & WebUI through GoodCloud.
Strangely, I have to try two times before it works, the first time I click to access the WebUI, I get a Request timed out message.