In writing up some instructions for teachers, I inadvertently did not enable the Gradebook for an assignment which was configured to receive online file submissions from students.
After impersonating a student to submit the assignment, as the teacher I could not see the 'Allow Resubmit' button.
After completing everything again only this time configuring the assignment to be added to the Gradebook, it was then that I could see the allow assignment button.
There are many of our teachers who do not use the Gradebook and therefore wouldn't think to add this as part of a file submission assignment. This would be problematic as once 1 student submits the assignment the gradebook settings cannot be changed.
Teachers should have access to the 'Allow resubmit' button regardless if the gradebook has been configured on a file submission assignment or not.