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I am having trouble envisioning polenta breaking, kinda like mashed potatoes breaking. I am not quite understanding the situation as you're trying to relay it. My brain processes things better with visual input than it does with verbal. Wish I could be more of a help, but at this juncture, it ain't happening.
With cream, cheese, and butter in there you have a lot of fat which upon reheating is going to want to separate out. Be gentle when reheating it by adding water to make it somewhat soupy and use low heat and stir often, as it come s back up to temp, water will simmer out and it will come back to the consistency you want for serving.