I'm having a similar problem with just one course in Moodle 3.9.6. In every other course, switching role to student and then scrolling to an assignment shows the Add submission button. But, in this one particular course, the Add submission button doesn't show. Neither do the Submission status, Grading status, Due date, etc. Just the description then nothing. But, in other courses, when using the Log in as student feature, I *do* see Add submission. I've checked the start / due dates, file upload is enabled, etc. I imported an assignment from another course (that *did* show Add submission when using Log in as student), and in the problem course the button did *not* show. Then I did the opposite, importing the assignment into another course, and then it *did* show the Add submission button. I tried creating an assignment from scratch, and it *didn't* show Add submission. The content in the problem course was imported from another course, could that have an effect?
I'm very confused! Anyone have any other thoughts? Cheers?