OLAP error processing the cube

Getting the following error

Errors in the OLAP storage engine: The attribute key cannot be found when processing: Table: 'Fact_Order', Column: 'Picked_x0020_Date_x0020_Key', Value: '12/31/2018'. The attribute is 'Date'. Errors in the OLAP storage engine: The attribute key was converted to an unknown member because the attribute key was not found. Attribute Date of Dimension: Picked Date from Database: WideWorldImportersMultidimensionalCube, Cube: Wide World Importers, Measure Group: Order, Partition: Order, Record: 52. Errors in the OLAP storage engine: The process operation ended because the number of errors encountered during processing reached the defined limit of allowable errors for the operation. Errors in the OLAP storage engine: An error occurred while processing the 'Order' partition of the 'Order' measure group for the 'Wide World Importers' cube from the WideWorldImportersMultidimensionalCube database.

Start by reproducing processing for the 'Order' partition of the 'Order' measure group in the WideWorldImporters cube. Investigate the missing '12/31/2018' key in the Date attribute and the Fact_Order column 'Picked_x0020_Date_x0020_Key'; the issue does not name files or tests, and done would require a confirmed correction that lets processing complete without the reported error.