Submit button not displaying after update

I am having the same problem, but i found the culprit and two workarounds.

My problem
After an update, our simple, one-page quiz was no longer showing its submit button.

The bug
Upon inspecting the code, i found that display of the form footer is oddly connected to the “Random Questions” option: when that option is set to “Disabled”, the code will append the qsm-d-none CSS class to the end section of the quiz, where the submit button is contained. This CSS class will disable display of the section, thus hiding the submit button.

Workaround 1
If you’re OK with changing the order of the questions and/or answers, just set “Random Questions” to anything other than “Disabled” and the submit button should show up again.

Workaround 2
If you’d prefer to keep the order of questions and answers, you can use Appearance > Customize > Additional CSS to append this here CSS rule:
.qsm-quiz-form>.quiz_section.quiz_end { display:block; }
This should overrride the effect of qsm-d-none, marking the end section always visible – so do check your forms for any undesirable side-effects.