Firstly verify that there were values uploaded and that the VDT is configured correctly. 

After confirming the above, you will need to check the selected benefit calculations for all KPI nodes.

If the selected method is No Impact on Benefit,  as displayed below:

The system will use the KPI Actual as both the Actual and Baseline on the benefit calculation thus resulting in a 0 improvement,  depending on the Root nodes' formula this will result in zero benefits.

To correct this you will need to make sure that Benefit Calculation for at least one of the KPI Nodes is set to Baseline vs Actual.