How do I create Closed Captions from a Source Monitor Transcript?

I am using the new transcript-sharing workflow described here. My end goal is to have my copy editor make any edits in the .txt file, import that back into Premiere Pro, create the captions in PP, and then export those captions back out to a .srt file to upload to our video hosting platform.

I have no issues when using the Program Monitor transcript but do have issues with the Source Monitor transcript as the create CC icon is greyed out. 

Any thoughts?