Obviously, successful use of authors notes depends on the story. But, they're also a great personal, informal way to chat to readers.
Authors notes are only relevant on the most recently published chapter. I've gone to edit old parts on this guide and in the authors note I'm saying 'Happy Easter'. In fiction, typical old authors notes commenting on, and apologising for, how it took too long to write, is irrelevant. And although separating them- E.g. in bold, italics or with icons of ------ can make it better, for me even separated from the story an authors note still halts the plot's flow when the next chapter is published.
It seems more professional when no authors notes are included because published authors include one at the end of the book. I prefer the way stories read without them.
Though, they can spark conversations in the comments between you as a writer and your reader, where you might have ended your authors note with a question. I have noticed that compared to the stories I've previously published with an authors note at the end of each chapter, they tend to get more comments than stories I've written without an authors note (although these are no longer uploaded).
At the end of the day, Wattpad is a community, and if using authors notes proves as a way to make friendly connections with other users that should definitely be enjoyed.