A family of Microsoft word processing software products for creating web, email, and print documents.
I'll start by saying that I don't see the behavior you see. I reproduced your table, and the repeating section plus sign is visible on every row, including the last one, no matter how many rows I add. I'm using Version 1609 Build 7369.2055 (First Release for Deferred Channel). I also see the same thing in Version 1611 Build 7571.2042 (First Release for Current Channel). If your Office isn't up to either of those builds, make sure you have all current updates.
As a workaround, you could add a narrow empty column to the right of the Assigned column and turn off its borders. Then you should see something like this: