Hi! Sorry for the late response. I'm not really sure of the process to appeal. If you go and meet with the Admissions Office to get feedback normally (which they usually do, but not sure about now in pandemic times), they will tell you what part of your application you need to improve on. For example, if they say your interview didn't go well, that might be what caused you to get red flagged. I mentioned the Mock MMI just as an example of the many places where professionalism is noted. Like someone else said, it could have been a reference or something else?
Sorry, hope this was somewhat helpful.