Ohh yes. Most definitely the list got deleted at some point or the relay that had it got busy, was offline and didn't send on time. Then Amethyst started a new one when you added a bookmark.
Discussion
Okay, right, so that's how the mechanism works. That makes sense. Good to know.
The same happened to me, all the bookmarks(private + public) are gone. So I assume there is no way of getting them back?