As you're migrating to the new forum, there's a setting that you might want to change, either in your new profile or by thread, as it'll let you see all the messages in a thread (as you can in this forum). I'm going to paste in ME's description of how to do this:
That's a preference you can change. Just go to User Control Panel and click Edit Profile, from there click the Feature Preferences tab and your first option is Viewing Preference. I'm guessing you have that set to Tree and you would prefer Flat. Don't forget to click Save.
You can also bounce between Tree (Thread Reading Mode) and Flat Reading Mode view by clicking on Thread Options at the top of the thread.