We had a brief situation where notifications coming from open teams were sent to every guest in that organization. That was resolved. Those notifications (email and push) did include the texts of the messages but at no time were the guests able to access the actual team content. That's why you are seeing the deleted messages. Those are to teams that you do not have access to so when you try to go to those messages you see the deleted error. All the data in your account is safe. Mostly you are probably seeing messages from our tenant as our support teams are all open teams and we have thousands of guests. We are drafting a complete technical explanation and will be posting it in a variety of locations to notify everyone. I am very sorry for this error.