That website likely has some invalid markup that is preventing calibre from parsing the page. From a quick look, it looks like it uses invalid HTML comments that look like this:
<!—OVOLABS_2 START—>
note the use of the mdash instead of a double hyphen.
I fixed the recpe to take care of that.
https://github.com/kovidgoyal/calibr...7727e30fcb8ba8