The $HOME/public_html for the wikistats tool is a symlink to /home/gedda/dist. Traversal of this symlink to a Toolforge user's home directory does not work on the 2020 Kubernetes cluster because the Toolforge /home NFS share is not mounted into Kubernetes containers. This mount was not available on the legacy Kubernetes cluster either, so I'm not sure why this has not been noticed previously by the tool's maintainers.
A simple fix would be to copy the public_html content into the tool's home directory.