Oh no.... here's a couple of things to check and try
You've the most up to date version of the app
Collect from the nutcracker again
Force close a few times (Force close: double click home screen, swipe up and off the screen the thumbnail pics. This clears the app from device memory and the loading screen will appear again)
Did you buy the winter castle before the goal asked you? If yes another player said collecting and storing fixed it for them.
If it doesn't fix itself which sometimes happens then you'll need to reach out to Support who will unlock it for you.
S8 Support: Click here to contact S8 Support
I'll move this thread to the bugs forum where it will be seen by S8 so they are aware of the issue.
I just logged in and it's solved!
Oh that's fabulous news. Good luck with the rest of the event