This is a duplicate to it-shows-old-question-in-newest-tab (which was closed).
It happened yesterday for me too the same time as it did for the poster of that question. After a few minutes it was working again. Now it happens again.
In newest quesions tab, questions from yesterday are displayed.
Now it is working again. Time elapsed: about 10 minutes.
The interesting thing is that it happened yesterday at the same time.