Over the past week, there have been many reports of missing data for Google Postmaster Tools. From what we can see, it appears data on the Spam Rate, IP Reputation, Domain Reputation, Feedback Loop, and Delivery Errors tabs stopped updating for some folks around April 11th or 12th. According to information posted in an industry forum, Google is aware of the issue and working to resolve it. Some progress has been made, but no official statement has been made (seems to be par for the course with Google).
As of this morning in my own account, most tabs have data up to 4/13 (with a gap on 4/12) and data for 4/17, but everything between is missing. It remains to be seen whether the missing data will be restored. After a similar issue last September, Google was able to restore the data pretty quickly – hopefully that will be the case here as well.