Hi Emma, thanks for your reply.
We're using Moodle 3.5 and the feedback block on course pages. The original activity is on the front page.
I have figured it out!
My solution was that even though students are enrolled as 'students' on the courses, where the feedback blocks are. They are default users on the front page, where the actual activity is located. The role on the page with the activity is the role that is used when the activity is repeated using a block.
So, I had to go and change permissions for the default users role, so that role could respond to the feedback activity.
It would have worked by enrolling all students into the student role on the front page, but we have too many students to do that easily, and it doesn't support the enrolment setup.