Ah! For future reference, it would probably be best to give explicit credit to the artist in the series description and your beginning author's note. I know lots of people can be leery about stolen art on novel covers and many do report them if it isn't clear the author has permission to use the images.
If that is the reason your series is hidden for now, Tapas may still take a while to reach out to you. You can try e-mailing them at feedback@tapas.io to clear things up.