I've tried un-registering and re-registering and it just keeps getting stuck. No logs I can see so I'm not really sure what to do...
Has anyone experienced this before?
It appears that there was some issue, which is now mitigated. Check your Service Health/Resource Health page.
The ‘Service Health’ - Service issues view shows any ongoing problems in Azure services that are impacting your resources. You can understand when the issue began, and what services and regions are impacted. You can also read the most recent update to understand what Azure is doing to resolve the issue.
Resource health helps you diagnose and get support when an Azure issue impacts your resources. It informs you about the current and past health of your resources and helps you mitigate issues. Resource health provides technical support when you need help with Azure service issues.
Reference:
https://docs.microsoft.com/en-us/azure/service-health/resource-health-overview
If its a brand new subscription i always like to deploy a new Resource manager VM to register all the required resource provider. Once the VM deploys OKs then you can try the AKS (Kubernetes) deployment.
Note: you might still need to register Microsoft.ContainerService for AKS
While you wait for support you can try that an see. Don't forget to delete the VM.