Are you talking about breakfast Saturday morning or Friday morning? If your staying Friday night, then the hotel doesn't even have to give Plats free breakfast then. The elite benefit is for breakfast M-F mornings. Unfortunately, it doesn't include weekends.

Now if you are staying Thursday night and they won't provide you breakfast on Friday morning, then that would be against Marriott's elite benefits. I would then suggest you call the MR elite line and ask them to talk with the hotel to make sure you get the breakfast you are supposed to get.