That takes me back

-- it bit me when I first started messing with permissions in MODx. Our resident permissions expert (sottwell) is otherwise engaged so I’ll try to explain.
If you want a document public for the public, so to speak, it can’t belong to any document groups that are tied to web user groups -- *manager* user document/group connections have no effect on public access.
Web permissions and Manager permissions are separate and, in either, as soon as a document is assigned to a document group that is connected to a user group, it can only be accessed by users belonging to that user group.
If you have a bunch of these to fix, try using the DocManager module (click on the Modules tab).
Check here for more info on permissions:
http://wiki.modxcms.com/index.php/Document_Access_Permissions