So, now that Halloween is over, it seems that it took the achievement categories with it. In my Historical tab there should be 2 for Shadow of the Mad King (the original, and the most recent Halloween), and 2 Blood and Madness (for 2013-2014). But, there is now 0 Shadow of the Mad King, and only 1 Blood and Madness.
This doesn’t seem to have impacted my achievement score, but I would like to have the visibility of these categories restored.