The problem has been fixed, but it does require you to go back to your Matching questions in the Item Bank and edit them. You don't have to modify any existing assessment, just the Matching question itself.
Once you edit the question in the Item Bank, you will see a message stating "Some students have already submitted answers for this item! You can apply your edits to a copy of this item which will only be seen by students that have not taken the assessment."
Select Edit a Copy.
Please note: I never saw a duplicate of the question in my Item Bank, so the concept of a "copy" didn't really occur visually to me. I believe it was just handled in the background of the system.
Once I edit the Matching question, I look for the Grading option and select Partial credit and the click Done to save the changes.
This method worked for me and I hope it works for you as well.
