Cluster explorer is white page Rancher with AKS

I have an installation of Rancher v 2.5.9 in an AKS cluster.
It looks like Rancher is able to provision downstreams clusters in AKS but cluster explorer in Web GUI shows nothing. There is just a blank screen for every deployed downstream cluster. It is not possible to operate downstream clusters.

The main AKS cluster however is shown fine in the cluster explorer.

What is wrong? How to troubleshoot this situation?