The completion type is whether the activity is marked as complete manually (by the student ticking the standard manual completion box) or via completion rules (such as the student ticking off x% of the items in the checklist).
However, neither of these are directly relevant, as it's not the editing of the checklist settings which is the issue, but the editing of the items within the checklist.
I've pushed an update into github which should fix the issue whereby switching an item between optional and required (or adding / deleting an item) did not update the student grades for the checklist (even though this action does affect the calculated percentage and, hence, the grade).
I didn't want the grade recalculation to run for every change to the checklist items (on a course with a lot of students, this could noticeably slow the process down), so, instead, I'm queuing up a background cron task to do the recalculation (triggered by a relevant change to the checklist items - I don't trigger it if the checklist has just been rearranged, without adding/removing items).
Are you able to test the code published at
https://github.com/davosmith/moodle-checklist to see if it solves your problem?
(This update will be published to the plugins directory in time for the Moodle 4.0 release - I'm not going to do an extra release, with that being so close at hand).
