@CelesteCunningham has a good idea.
I also agree you should not risk identifying DS, OP, but as things stand it is hard to understand what happened. Is it possible that the new academic who marked DS overlooked some of his contributions? If so that is certainly worth raising, politely, in his informal conversation.
It is well within the remit of his personal tutor or academic adviser to give an informal view on how best to proceed. Particularly if there is any chance that work has been overlooked. @CelesteCunningham suggested the best approach.
OTOH if DS doesn’t really know this person or if they don’t respond within a few days, he should contact a Student Support Officer in the Teaching and Learning Office.
Gently, again, best to focus on his own case. The issues as far as I can see are (a) whether he has grounds for appeal per the first term episode and (b) whether any marks were overlooked on the recent project. He needs to stay well away from appearing to question academic judgment.
(A poor rubric may or may not be grounds for appeal - just a thought.)
Being marked by a new academic who may have interpreted the rubric a bit more strictly is just one of life’s pieces of bad luck. The marks have presumably been externally moderated and found acceptable, but external moderation would not necessarily pick up a gap in communication if indeed that is the problem.
I am a bit concerned I don’t understand the project well enough even to be saying this, so proceed with caution. Best wishes to DS.