When you mention "dashboard," are you referring to the Application Dashboard (flow map) or a custom dashboard you've created under "Dashboards & Reports?"
If you are referring to the Application Dashboard (flow map), please navigate to Tiers & Nodes and ensure your agent is online (App Agent Status shows an up-arrow), indicating the application agent is communicating with the AppDynamics controller. Also ensure the application is under load for the time range you have selected, as the flow map is dynamic and can turn blank if there is no application load to visualize.
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