Hi. I was able to experience the issue and it seems that when you changed DemoReplyWidget to GameReplyWidget in the GameDialogueWidget, you forgot to relink the ReplyNode variable. This link between Array Element and Reply Node as shown on the screenshot was not present in your project.
https://i.gyazo./20251a53dff66c2c8aa3a12a68232632.png
Cheers,
CS