We are having similar issues. The advanced levels seem to go away from day to day... but not always. The little + & -symbols for selecting difficulty level lose their green shade so there is no longer an option to select advanced or expert for some games. It's sporadic, but happens more often than not. Additionally, we're finding that the advanced levels, once they've come and gone away, do not seem to unlock again as easily as before.
Is the is feature? A bug? Are we not looking in the right place? There's gotta be a trick to it, right?