I've had a similar problem today. I connected my Flic Hub to the Ethernet port while being connected to wifi. Then I disconnected wifi from the mobile app. I clicked on Test Connection and confirmed the Internet access however Ethernet was showing not connected in the app however I couldn't log in to the SDK. While the Flic Hub was powered, I removed the ethernet cable and plugged back in and it reassigned the IP. Then it worked.

@theo I think you need to add the http:// prefix to the url.