By chance I tried to build our PDF docs on a Fedora 30 installation, and it doesn't work. xsltproc seems to get hung up in a tight loop before it starts to produce any output. The HTML build works fine, though.
Relevant package versions: docbook-style-xsl-1.79.2-9.fc30.noarch libxslt-1.1.33-1.fc30.x86_64 Anybody seen this, or have an idea what to poke at? regards, tom lane