3D FlipBook - Special PDF cannot be selected with Safari

Hey there, I've just started using the free version of 3D Flipbook and have a problem when creating a new book in Safari. There is one new PDF (https://www.muenchner-feuilleton.de/wp-content/uploads/Muenchner-Feuilleton_Nr_117.pdf) that can't be selected. If I try to select this one the site reloads and the pdf-url-field is empty again. All the other PDFs work fine and there is no problem in Chrome. Just want to let you know and maybe you have an idea?