Submit All Not Working

Here's my latest problem:  we have a module which is basically just a quiz using random questions from a single pool.  The only slides are a title slide, an intro slide, 20 random quiz questions, a quiz results slide, and a final "here's what you have to do next" slide.

In preview modes and even when published, it lets me navigate around as expected, answering all the questions, and when they're finally all answered, clicking on Submit All seems to do nothing.  The button doesn't even react.  It's like it's made of wood.  I am not sent to the quiz results slide as I would expect, but I can continue navigating through the question slides and can even change my answers, which maybe is not surprising since the Submit All button doesn't seem to be active at all, even though I've answered all the questions.

Does anyone have any idea how I might fix this?