Itamar Tzadok

Not sure what the link is.

a) There is no special preset. It's a standard Dataform activity which you can build in any way you want. The "trick" is a designated availability condition plugin which allows you to set a condition on the existance of entries for the current user in the target Dataform. I've just drafted the plugin and it's incomplete and has not been released yet. But it works enough to prove the concept.

b) Standard Dataform feature: Dataform_building#Preventing_participants_from_viewing_other_entries.

I've just drafted a much more flexible way. Not surprisingly it involves the Dataform. The idea is to use a Dataform instance for assigning activities on a personal basis. The instructor adds entries on behalf of students such that each entry unlocks the respective activity for the student. The advantage of this approach is that you can use any activity/resource as a tailored material. And in the Dataform you effectively store a list of the assigned activities per student. You can also add instructions and other personalized information and allow the student to record feedback on the activity. Etc.

Pictures may sometime be worth a thousand words or at least add a bit of credibility to those thousand words. A quick illustration below. Goes without saying (for those who are familiar with the Dataform module) the illustration is but one possible use of this approach. Other possible uses or extensions are allowing students to choose their extra activities, adding bonus marks by number of extra activities, etc.

Instructor's course view

Note that two of the advanced activities remain visible to students when unavilable and the third is hidden.

Instructor assigns advanced activity to Jane

Jane's course view

Jane has access only to the Extra practice quiz that was assigned to her. She can't see the Group choice activity because that activity was set to be hidden unless unlocked.

Jane's list

What would be the simplest scenario (initial conditions, list of steps, outcome) to reproduce this problem?

Try the Dataform module if you don't mind some learning curve. Not sure how it would work with checkboxes but with dropdowns you can definitely have a form with a number of question and then display totals of subsets of the questions. You can find a related discussion at https://moodle.org/mod/forum/discuss.php?d=270973.