WBS Element missing in COPA Datasource in BW

Dear Gurus,

I am facing an issue about missing WBS elements in BW. I am using COPA datasource in BW and when I am extracting the data, I see that in some records WBS element is missing. But when I go to the base table of COPA in the ECC system, WBS element is available against that particular COPA document number.

I haven't done any modification in my datasource but still WBS is missing. Can anyone help me in solving this issue?

Field for WBS element in COPA is PSPNR.