Completed daily challenges vanished?

So, I've been doing this since the end of season 2 and never had a problem. I save up my daily challenges during the last few days of each season, complete them, and collect them when the new season begins. For some reason, I completed my challenges today, and when the shop items reset, it deleted 2 of my challenges and replaced it with a new one. Now, I know it's only 1.5 tiers, no big deal, but I'm just wondering why they deleted like that and if I got the xp from it?