I'm not sure when this changed, but currently, if a student submits a file under and assignment, Populi isn't always marking it as a submission.
Specifically, if the student drags a file to the middle of the submission page (where the big drag and drop box is), Populi will consider it a "submission."
However, if a student drags a file to the smaller "drop an attachment" box on the right column and they click the "submit" button, Populi will not consider this a "submission." This doesn't make much sense since the student has clicked on a "submit" button. I see that after a student uploads a file, they can subsequently make two more clicks to "set as a student submission," but that process is not obvious, so students are not doing it.
The result of the second means of submitting a file, is that when I click on an assignment name to see who submitted assignments, Populi does NOT have a check mark on the right side of the table under the "file" column, and it looks like the student hasn't submitted anything, even though they did upload a file and click on a "submit" button.
In sum, please make any file that a student uploads under an assignment automatically be marked as a "submission".