What kind of access do each of the apps have? For instance, it sounds like apps "Bbb" and "Ccc" may be registered for the "app folder" access type, so they'd only have access to the contents of the special app folder that gets created for them when connected to an account, not anything else already in the account.
When you use an access token for an app folder app and try to access a particular path, that path will be interpreted relative to the app folder for that app. For example, if you send "/Some Folder" it would be interpreted as "/Apps/<APP FOLDER NAME>/Some Folder".
So, if you used an access token for an app folder app to try to access a folder in the actual root of the account, for instance, it would fail like this because it would only see the contents of the app folder.