Earlier last week we identified an issue with ExchangeDefender whitelists. At first we believed the issue was simply that of certain notes not receiving full replication but after that turned out not to be the case we focused on the internal processes that generate note whitelists. The problem turns out to be a bug in the replication of whitelist content between users and master whitelist.
We have been working on it through our maintenance interval but have added a few more hours for additional testing today to make sure it is working properly. As a result of the bug we have rewritten how the whitelist data is replicated and as a result monitoring scripts that watch for replication failures had to be adjusted as well.