The Chairman’s Bao is a graded Chinese reader. You can find it here: https://www.thechairmansbao.com
As for the LingQ API: I agree. In fact, the site can actually do much more than the API. Not only that, the API is very poorly documented and clearly not officially supported by the developers, as some functions don’t even work.
The only reason one should use the LingQ API is for mass-importing of lessons. I don’t think you’d want to sit there and hand-import three thousand articles 
Not only that, there’s no way to actually know what the invisible words were. They don’t show up in the vocabulary section nor anywhere else I’ve been able to search through.
It really shouldn’t be this way - we should be able to rely on our statistics and not be afraid to mark lessons as complete.
Thank you 
I think they arent actual words. Most likely they are weird signs that are not displayed on the lingQ platform, for example heart signs or arrow signs etc
They might be signs in some cases, but I only read news articles and children’s stories, neither of which use arrows, emojis, etc. They are just raw text with proper punctuation.
The cynic inside of me says that this is an intentional “bug”, one that gives the user a false sense of growth when really they’re not making as much progress as the numbers say.