Serial Number disappears after releasing the model

Hello there,

while trying to set up my company's PDM PRO  we have set the workflow and a serial Drawing Number in the drawing data card.

As soon as the  drawing gets released (or approved as stated in our workflow) the serial number disappears. 

I am attaching our workflow as well.

Could someon suggest us a solution please?Do you have any idea why this is happening?

Thank you in advance for your time.

SolidworksData Management