Well, invisible? It's only visible if you select the surrounding text, like above: The thin red line after 2016.
It behaves like a hard return. It's not much of a problem, but I'm curious what it is, and where it comes from. The original file format is HTML, so that's obviously where it comes from, but how?
It also shows up in Auto-Completion, except that it doesn't show because... it's invisible. Strange.
Did you already try to identify it?
Please see this article. It might help you determine what the character is.
cafetran.training: Did you already try to identify it?
No I didn't. Never thought of the Unicode identifier. It's: U+2028, line separator. That makes sense. Though it shouldn't be there, should it?