The problem was that the rendered content of the HTML element is only as wide as the parent element, which caused me some headaches as the content of the PDF (like the tables and text) were cut off at the width of the parent element.
The parent element was – in my case – simpy as wide as the browser’s viewport, which is kind of bad on a mobile device. So I tried several things – without much success. At last, I have had to use a dirtly little hack to make the canvas/render area wider.
I simply inserted a div with a fixed width of – in this case – 1500px. That fixed it for me.