> Our caching ruleset was not obeyed by our CDN partner. [...] Before the site was shut down, you may have viewed some pages as another user.

What CDN would not respect "caching rulesets"? Cache-Control: Private and Vary: Cookie are well-established.

> We will follow up tomorrow with a further technical explanation of what occurred.

I can't wait. I hope they're being honest and this was a genuine error of a third party, and not incompetence on their end.