The grouping will only be for the big fandoms, if it happens i.e. if there are more than 5 secrets of the same fandom in the same day's batch. So if there were 20 Doctor Who secrets, they would be grouped together. If there were 4 Supernatural secrets, they would be kept random.
The rest of the post would be random as usual, so the randomness would never be completely lost.
The secrets will continue to be picked in random order from the week's batch.
SO, secret grouping: