The sauce broke?

A sauce breaks when the fat and the liquid separate, making glops of fat separate from the flour, instead of being smooth and velvety looking. A sauce can break if the fat is added to fast, if it gets too hot, if it is not served soon enough, or if it is refrigerated.

Thanks!
I've never heard the term ... though I understand the results and the causes!

Also "breaks" when cooking it too long, after the milk/cream is added.

One of the ways to help avoid is to make a roux, then add the liquid ... and adding the milk/cream at the end after the sauce is formed.