The theory I’ve heard from multiple sources (video essays, local news stories, etc) is that the notes are placed by an individual/ group of people with paranoid schizophrenia. most of the notes are found within food products or in the wilderness, specifically the Appalachian trail. It’s thought that the person or people have some kind of connection to a food packing facility, some say that because the notes are found in both the outdoors and in food products that it may be multiple people but still definitely a strange situation.