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:

I am not sure if this is just a technical revamp or a complete revamp on how Google sends and manages these notifications?

Update: John told me, “We’re just making things a bit cleaner and more consistent – nothing crazy.”
Forum discussion at Google Webmaster Help.