This reply is very, very late. But, it may help someone else. I only bought this EP a couple of days ago and my Sim did not get her degree.
I went back to a save just prior to her graduation, reduced the invites to three or four and played the last day through again. She got her degree and her extra trait.
I have another problem though. My sim was allocated "Avant Garde" for her Social Group trait so, I elected to change it. It did not change. So, I went for another social group but, it would not change on the second or third attempt either.
. Finally, I took my Sim Back to the pre-Uni save and played it all through again. Still no change. BUT, I did have the "No Degree" problem again! So, once more back to repeating the last day. This time it took 2 attempts, so, I am guessing this is a common bug.