by Christos Chris.
Hello Mary, thank for your quick response.
Yes, I have imported the course in Moodle. Basically I create one course and then I cloned it 5 times. (backup and then restore)
I tried your suggestion. I found that if I make one small change (I set allow Submission comments to Yes) to the activity settings the button appears again.
So there is no other solution? Everytime I import a course I will have to edit the assignment activities and press save?