Special:LinkSearch will not return links after the first 10,000. You were previously able to manually change the URL in order to display them, but this no longer seems to work.
Eg. https://en.wikipedia.org/w/index.php?title=Special:LinkSearch&limit=5000&offset=5000&target=http%3A%2F%2F*.highbeam.com is a functional link, but https://en.wikipedia.org/w/index.php?title=Special:LinkSearch&limit=100&offset=10000&target=http%3A%2F%2F*.highbeam.com returns "There are no results for this report" (and there should be results). https://en.wikipedia.org/w/index.php?title=Special:LinkSearch&limit=5000&offset=6000&target=http%3A%2F%2F*.highbeam.com returns 4000 results rather than the 5000 results requested (And again, I know that there are results beyond that).