Well, according to the Wall Street Journal, it falls victim to an algorithm with absolutely no sense of irony.
A video titled "The Dark Art of Political Intimidation" was posted last week by WSJ columnist Kimberly Strassel as a PragerU lecture. "Within several hours of PragerU posting the video," said a WSJ editorial, YouTube placed it in 'restricted mode,' making it inaccessible to schools, libraries and young Americans whose parents have enabled YouTube technology filters."
Conservative radio host Dennis Prager's idea for PragerU is to give students alternative, non-progressive takes on history, civics and other issues. Of the 100+ PragerU videos, YouTube restricted 18 of them, even though there's no cursing, no violence or any kind of indecency in any of them.