In version 3.6 of the guidelines the icons of the severity of rules are shown in the PDF:

In version 4.0 and 4.1 the icons are lost:

The reason is that the CSS is not understood by wkhtmltopdf. See alsowkhtmltopdf/wkhtmltopdf#3253 . As a result a workaround must be found to get the icons back. Probably by patching the generated HTML and/or the CSS files.