Looks like the page wasn't able to load all of its resources. Try to refresh the page until it works. I should make an offline version that doesn't require online processing.
Is there a PDF version?
The document uses a JS tool called MarkDeep to convert extended MarkDown into styled HTML. Just look at the source, it's 99% plaintext Markdown.
If you read the MarkDeep docs, you'll find that it has a feature to convert the source into PDF instead. I admit I haven't tried this, though.
If it were up to me, I'd do the transform offline and just serve the static HTML instead. And sure, a link to the PDF just to be nice :)
Why is it still so hard to design a page to load reliably?