If there's no post within a week (?) a room gets frozen. But not if there's no post within 15 hours. Check the time between your unfreeze (16:15 yesterday) and the next freeze (6:58 this morning).
Seems like a simple unfreeze is ignored unless followed by at least one post to reestablish the intervall again. That's why I usually follow my unfreezes with at least a one-liner.
Call it global warming if you like – but I don't like to freeze :)