Did you just add the new node or installed a data node on the new node as well. If there is no data node on the new node then you may not see the data. Just click on the newnode link and see what all services are listed.
Can you please check if the following API call is returning any value there?
# curl -u admin:admin -H "X-Requested-By: ambari" -X GET http://localhost:8080/api/v1/clusters/Sandbox/hosts?fields=Hosts/host_name,Hosts/disk_info,Hosts/os_...
Please replace the "localhost" with your ambari-server hostname
Also the "Sandbox" with your ambari cluster name.
Also let us know if the OS and Python version and is same across the cluster (Specially on the new node)?
# python --version Python 2.6.6 # rpm -qa | grep ambari
If you see that the Host Summary in the UI shows "Disk: Data Unavailable" (On mousr over) then one of the reason can be that the Ambari Metrics is not installed. In that case please check if that host has the "Metrics Monitor" component installed and running. Also please restart the ambari-agent on that host.