Backtrack here, because now I see the problem. It's interpreting your query string as part of the URL. Or, in the alternative, your site is coded so the part beginning in ? isn't getting interpreted as a query.
What's the "real" file format behind the extensionless URL?
A moderator will come along presently to change your domain name to example dot com. But the underlying problem will still be visible. Meanwhile I have been to the site and confirmed that the unescaped version works, the escaped version doesn't,* and the queryless version has a link to the troublemaking version.
I assume you have lots and lots of these and the same problem occurs everywhere. Is it always just one question mark and just one equals sign? If so, the fix is trivial. But I want to get at the underlying issue.