Unfortunately, in early March, Facebook changed the comments display from chronological order to "social relevance" order. In this new ordering, Facebook determines what should be at the top of the comment box depending on the user that's logged in, amount of Like's per comment and other factors.
Though there have been many complaints and requests to Facebook for it, there's no way to set a default of chronological ordering to the comments. Right now, the user can sort the comments by clicking in the top left corner of the box where it says "10 comments", and they will be presented a drop-down with new options to sort.
The best suggestion we have, if this is critical, is to put a note at the above or below the comment box calling out that comments can be sorted this way.
Originally, when the new comment box was launched, there was no way to do sorting.. it was social-relevance only. We're happy they added the sorting drop-down, and hoping that they will soon add a default sorting option that admins can choose as well.
Thanks,
Alex
How to sort comments
