Actually, it is working.
You'll notice that it's blocking out the the lead paragraph. That's how things are set up on that page. The nature of the spoiler javascript is that it blocks the first <div id="SpoilerAlert"> that's on the page. Currently, that div only includes the first paragraph.
You may be remembering an earlier form of this code which blocked the entire page. But the code now works on a per-first-div basis, and that can't be altered.
Of course, we could expand the amount covered in that first div, but it can't be the whole page.
Besides, the question now is, how much of that S11 page really needs to be covered by the spoiler warning? And is it really the lead paragraph? I suspect the spoiler warning needs to be taken off that first paragraph and probably moved to the section detailing not-yet-broadcast episode titles.