PMs never received, where do they go?

[sirio11]

Between 0 and 7AM, I received 4 email notifications that I have a new PM in 2+2, but no PMs were found in my 2+2 account, after 7AM, things were back to normal, and for every email notification there was a PM to be found. Where did these PMs go? Is there any way to retrieve them? First time I notice this happen. Does this happen frequently? Of course I don't expect 2+2 to be Yahoo or Gmail, just wanted to know if anybody has had these problems.