I look at my subscription list and notifs occasionally, and I noticed this one user that keeps appearing on my subscription notifications. But when I go to my subscriber's list, that user isn't on there. Why would someone keep subscribing to my story(presumably to read it?), just to unsubscribe later? Has anyone experienced this?

edit: I should have worded this better. This user isn't subscribing just one time and then unsubbing if they don't like it. They're subscribing again and again to the same story and unsubbing later, and this happened over the course of a few weeks.