I am not seeing that problem and have not received any other complaints, so it seems it is likely something with your browser or computer causing the issue. If you haven't restarted your computer, I'd suggest you give that a try to see if the Reply buttons display then. If that does not help, then clear your cache and cookies. If you need help with how to do that, you can refer to this Help answer: www.sparkpeople.com/community/help_answer.
I hope one of those tips helps!