For you editors, there's head-hopping that could be annoying and then there's head-hopping that is flat out confusing. I'm reading a story now that is filled with head-hopping, but it's the second type that I'm posting about. Something you should look out for when editing.
I won't mention the story or use examples from the story that someone can use to do a search and find the story because it's actually a good story and well-written except for the head-hopping.
The author has a tendency to not only head-hop (jump from one character to another), but does it when a new scene occurs without a scene break. So you're reading something and then there's a dialogue that doesn't fit. You find out it's a character that's not even in the scene. That's how the author jumps from one scene to another.
Imagine Character-A talking to Character-B in school. And then there's a dialogue that doesn't make sense. You find out it's Character-C talking to Character-D somewhere else. And the dialogue doesn't even have a dialogue tag so you have to read a few paragraphs to understand who's speaking and to whom and where and when. It's the most jarring and confusing head-hopping I have ever come across and is probably easier for the editor to spot than the author.