I spotted a thread at the Google Webmaster Help forums where Google said they have started revamping all the the messages/notifications sent via Google Webmaster Tools.
Google's John Mueller said this in response to a webmaster receiving a delayed notification. John explained that they paused some of the notifications during the process of this notification revamp.
Here is how John worded it:
Recently we've started revamping all of the messages that we send to the notification console and via email and have paused email delivery of these while they're being reviewed. I believe this would have included the messages that were recently sent to your Webmaster Tools account. Sorry for the confusion in this regard.
I am not sure if this is just a technical revamp or a complete revamp on how Google sends and manages these notifications?