When a data stream has a consistent Y-axis value, the result may not register for the graphing component by default. However, this data is still collected and available for the report(s).
As a workaround, set Autoscale to False in the AxisY section of the report's Properties.
NetIQ Technical Support has recognized this as an issue and is currently reviewing it. This article will be updated to reflect the most recent progress.
When selecting a single metric for a report that has one constant value in the entire data stream for the Y axis, the graph's Y-axis will not render a label.