I wanted to share what we experienced archiving enrollments for our retired courses.  We logged a ticket which was helpful but we received an error and finally I figured out a solution.  Since you can only archive up to 10,000 at a time and the select all wasn’t working, I did a filter by for ENROLL and then I selected all and unenrolled them.  Then I filtered on IN PROGRESS and COMPLETE and then archived. I’ve had no issues going this route.  Only thing to remember it’s a background job so it’s not instant like unenrolling.  I just truly wanted to share in case someone is having the same issue we were experiencing!