Clearing the DNS cache "only" isn't a magic fix (followed all the examples in the cPanel DNS cache clear instructions, and that didn't help).
But, if you still have the affected sites showing up as down clearing the "browser history for the last 2 days" (or something akin to that) should fix it.
That's what worked for me on several computers.
Until your customers do that, you may have some who get the "down" page unless they specifically change the URL by adding /index.php or something to it. But if they clear their browser history they should be fine.
Strictly speaking, this symptom is no longer a Camelot-specific issue.