Hey Michael, just stumbled on this error again today as i was redoing the chat in our game, seems like you forgot to add the in the updates, just bumping this up so you see it again.
You did update the lineHeight property, but you forgot to change it in the UpdateVisibleText method.
Line 299 of UITextList
int maxLines = Mathf.FloorToInt((float)textLabel.height / textLabel.fontSize);
should be
int maxLines = Mathf.FloorToInt((float)textLabel.height / lineHeight);