@Costa I had the same issue with the "TV Season Premiere" holiday disappearing at 6 am. All of the "Surprise" holidays like Play The Lottery, Talk Like a Pirate, etc., disappear at 6 am on the day they are supposed to occur. This happens in two different cc/mod-free saves. I created a Bug Report just in case anyone else is having this problem.
I also have the disappearing harvestables bug in both saves.