The holiday items sort only shows if you click the "Show Holiday Items" popup you get the day before and used to stay until the holiday was over. Now it immediately disappear if you close build mode. This appears to be a bug.
I will say, before the category went missing, I almost never clicked the "Show Holiday Items" on the popup, and I still had the category every time I went into Build Mode between popup and the end of the actual holiday.
ETA: when I say "almost never," what I mean is that aside from the very first time a holiday showed up for me after I got Seasons, I literally never clicked that button on the popup.
