Earlier quoted context omitted.
I was going to say that somehow I knew I had to scroll the first time I entered. But I went back after reading your comment and I have no idea how did I find out the first time, there is no indication that there is content bellow.
Same for me. It was immediately obvious I should scroll, but I don't know why.
Seeing the timestamps change as I scrolled and seeing a progress "bar" update within the speech balloons during the dialogs made it more obvious I just had to scroll to see the content change.
I do think the progress bar color is low contrast enough that some might not see it and not realize they have to scroll to cause the dialog to update, though.