I got a "Topic reply:" email at 12:12 PM EDT. As long as I read the reply while logged on with my forum ID, I get more emails. If I get the email on my phone and jump to here from that email, it doesn't count as being read because I'm not logged into the forum on my phone.
If the forum doesn't know that it was you who read the reply, you won't get an more notifications on that topic.
When it doesn't seem to be working for me, I go to the
New Replies button and click either the
Last Post button for the particular topic, or the
Mark all messages as read button on the New Replies page. That seems to get things straightened out if it's not a site-wide issue.
You can also check the
Notifications section of your profile to confirm that you have notifications turned on, and for which threads.
Edit: This is also where you can tell the board to notify you even if you haven't read the last one, but that could get irritating if you're only marginally interested in a hot topic.