Linking a BOM Part Number to a Drawing Custom Property

Good Morning,

I'm attempting to drive a drawing BOM's part number and QTY for a particular item with a drawing custom property. The QTY seems to be linking without an issue, but the Part Number cell doesn't display the custom property text. It's just showing a blank cell. 

Has anyone had this issue before and what was the solution? 

I'm using the drawing for a DriveWorks project that will update the two custom properties as needed. 

SolidworksBill Of Materials