From experience, they are usually just delayed, though it could be a considerable delay (hours, maybe up to a day).
What I have been doing in the meantime is this:
Log into Mr.Excel, then go to the "View your posts" section.
This will show you all the threads which you have started/replied to. They are sorted by the time of the last post, so you can easily scan to see if there are any new responses to any of your threads.