The Single Choice Set in the interactive video is not being restricted to "single". In fact by default it starts with 2 choice sets. And when you are taking it, it is impossible to go next. In fact even if you remove the 2d choice set and only set 1, when taking it you can see that there are 2 steps. I assume the second would be the summary, but anyway, you do not get any feedback and its not possible to move to the "summary".
Im attaching an image so that you can visualize what i am talking about. I removed the second choice set that is added by default (that should not even display i assume?) and as you can see by the blue bar at the bottom, there are 2 steps, where i assume the second one would be the summary, but it is impossible to navigate.
Fix described SCS bug inside IV
I suspect the fix is handling when SCS has empty 2nd set or just 1 choice set