The board has a few bugs still in it from the upgrade. Are you talking about personal messages being deleted? When you send a personal message, it goes into your outbox. Once it is read, it will sit in the sent box and disappear from the outbox. If it truly being deleted somehow, then we need to know about it to look into the bug.
If you posted a message on the board between July 22 and about August 6th during the upgrade process, then it would have been lost during the upgrade.
