kolibri: Unattempted answers in a quiz should not show up as difficult questions?

Observed behavior

Unattempted answers in a quiz show up as difficult questions immediately upon learner opening the quiz.

In the above example all 5 questions are categorized as difficult even though the second learner has just started the quiz, and haven’t even viewed the questions 2-5.

Expected behavior

Label questions as difficult only after the quiz has been submitted? Or more complex one would be to have the viewed and skipped more than once as the threshold for unattempted question labeled as difficult?

User-facing consequences

Coaches getting overestimates about the number of difficult questions.

Errors and logs

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Steps to reproduce

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Context

• Kolibri version: 0.12.4b6 upgraded from 0.10
• Operating system: Ubuntu 16.04
• Browser: all

cc @rtibbles @indirectlylit (I did not put the milestone, in case the fix is out of the scope for now)