I removed the menu and footer from the printed version, and disabled the flex layout. Now the thing is more or less sensible, except for a couple of minor issues:
some of the timeline go out of the page on the left;
the timeline vertical bars are not rendered (apparently the browser do not like background colors)
At least using Firefox 63.0.3 under Fedora 27. I suspect this is the case for many of the other pages.
The old page was rendered better, so this might have to do with the replacement of a div tag with a section.