It probably is, due to the forum has a different url now.
Did you utilize the redirect scripts from the import? That may help with users/bots/etc that have the old url bookmarked.
Or you could create a custom 404 error page that redirects to the new forum url.
If you have access to the server logs you would see this error for someone that requests a page that does not exist anymore.
Then at least you could confirm someone is attempting to visit the site but was not successful due to a bad url.
Then also resubmitting to the search engines is another path.
