CreationEdge is correct that the URL format changed, but the different scheme for meta domains isn't all that problematic here (more on that in a bit) - what was breaking this was the move from URLs that start with
http:// to those that start with
https://. Please, feast your eyes on this:
substring(Comment, charindex('http://',Comment) + 7, charindex('/', Comment, charindex('http://',Comment) + 7) - (charindex('http://',Comment) + 7)) as [site]
...when the burning finally subsides, you'll find yourself blissfully free of the temptation to parse strings with SQL. Suffice to say, this did not extract the relevant domain from post history when there was a https prefix in play.
Fortunately, Jon Chan (with some help from m0sa and Craver) endured the searing pain and fixed this up a week or so ago, and the new logic correctly identifies both old http and new https links.
Now that just leaves the change in meta domains to worry about... And since the old domain name is still an alias for those meta sites, the system is able to retrieve the correct site given an old domain. The only flaw here is that since the query groups by domain, stats will be split between old and new metas if both HTTP and HTTPS migrations exist in the data. This is fairly benign, and made all the more so by the fact that the stats page defaults to a 90-day period... And we're well over 90 days past the HTTPS migration now.
...But if you really want to see it, there's an option for longer look-backs: