In the Desktop App some of my notes have this pink line next to them with a text line, others do not. I also access and Share this Notebook with others through OneDrive. The Notebook doesn't have any Sync errors. What is this?
Look like the edge highlighting for Shared Authors, although I am used to seeing it with Author initials next to it.... - Shared OneNote will randomly assign a color to authors when they make their first change, and Edge highlights their changes (Again in my experience normally with initials) so you can see who changed what last.
You can also sort by recent changes and Author by using the History ribbon. You should be able to use Hide Authors to make it not appear.