So I have done that, and I get
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Cron is properly configured. I have no issues with notifications. It is just that the submission comments of the assignment activity are not notified (the feedback comments work fine). I believe is because Moodle does not trigger submission comments notifications, so just wondering if I can "activate" them without touching the code (something like Site administration > Messaging... etc), but it seems it is not possible (perhaps this deserves a Moodle Tracker?).
Everything comes to the context. I have students that need to submit assignments, but they can submit just one or ten (or one hundred) assignments. Some of them prefer one big assignment, whereas others like several but small - and that's totally up to them.
So we need to "mark" them individually, so as a workaround we have set up Maximum Attempts = Unlimited and we use submission comments for the feedback of each attempt. It would be great if they receive a notification every time there is a new submission comment from the teacher.
(another thing we can do is create individual assignments, but this will be super messy and confusing).