Hello!
My advice is to contact support.
When you enabled Advanced Kubernetes Management, NKE installed management pods (not management agents) in one of the clusters you selected. After that, the IP of the master node of that cluster was added to Karbon's config files.
When you enable this future on another cluster, NKE deploys management agents that will connect to management pods that were already deployed before (in your first cluster).
When you deleted your first cluster, Karbon still considered that your management pods were alive behind the address of the deleted cluster. When you trying to create a cluster, this procedure fails, because management agent can’t connect to management master (you already deleted it with cluster but it still in configs).
In short, you need to edit the Karbon files, remove those IPs, restart Karbon.
I guess that for this feature you need some kind of "management cluster", where no production workloads will be located, and this cluster you should use for "service pods" like Advanced Kubernetes Management and not delete.
Oh nice, thanks you for helping me !