Google-sheets – Chronological ordering of checkbox in Google Forms

Still don't have a solution for how to directly get values of unchecked checkboxes, but I was at least able to write a function that compares the correct answer to the submission.

This splits the correct answer into an array then compares each item to the submission:

function checkAnswer(answer, key) {
var kArray = key.split(', ');
var nArray = [];
for (i=0; i<kArray.length; i++) {
    if (answer.indexOf(kArray[i]) == -1) {
        nArray.push(kArray[i]);
    }
}
return nArray.join(", ");
}

Then I could call it every time I needed to report the boxes left unchecked. For example, with the doors question:

if (doors != correctDoors) {
  var doorsMessage = "Unlocked: " + checkAnswer(doors, correctDoors);
  report.push(doorsMessage);
}

At the end, I'll compile the report with:

report.join("\n"); 

And voila! The best I could do...

Ultimately, I'm still looking for how to directly get the unchecked boxes if anyone has a solution.

The problem is in the first line of the script. Your form ID is the special ID that identifies the form. You can see it in the address of the form (it's the bit in bold)

docs.google.com/forms/d/17rxZ5vzy0OcxibXV6aRpso7Xm_Vs0FpxMLgbchjO998/viewform.

You accidentally used the form name instead.

That being said, I should have just used the Spreadsheet.getFormUrl() in the original answer. I'll change that now, then you won't have to worry about the ID at all.