Why would 1 of 3 search heads in a search head cluster not show any results in the distributed management console?

I have three search heads in a search head cluster and they are all listed in my Distributed Management Console as search heads. Only 2 of the 3 instances are showing data when viewing in the DMC dashboards. The introspection log on the search head not displaying has the data and the `index=_introspection` shows data for that search head. I am running Splunk Enterprise 6.3.2. Why would that one search head not show data in the dashboards? Thanks. Paul