This was because the slave db server stopped updating off of the master db server. You read off of the slave and write to the master, with a process that updates the slave off of the master. That process stopped, so while the master database was being updated, PM's are created, update emails are sent, people revieve notifications.... but the forum looks exactly the same. To further complicate the issue, the slave fails back over to the master, so sometimes it actually works... but then it brakes again.

This gets especially confusing with how logins are processed. The servers have been fixed and we do not expect this outtage to occur again.