How to remove the Unassigned column in Forecast Shipment Definitions Table

Summary:

We are trying to simulate Demand forecasting for a particular item in an Organization by loading sample shipment history with Demand class. After running the plan and reviewing the plan output, when we check the Forecasted Demand in the "Forecast Shipment Definitions" table, under the Demand class hierarchy, we see a column "Unassigned" for the Demand class. I have tried purging all the Shipment history for all other items except for the item that we are simulating, and yet we see the column "Unassigned" even though there are no data to be displayed under Unassigned demand class.

Can someone guide how this can be removed from the view or what should be done to stop this from being displayed on the Forecast shipment definitions table.