Figured out what is wrong and how to fix it. Instead of showing my usual Marriott 9 digit number (123456789), the website is now showing 123******. That box seems to be greyed out and I was unable to log in with that number or change it. However, if I scroll to the bottom, there is an option to "Clear Remembered Account" and that will get rid of 123****** and allow me to enter my correct number.

Just more Marriott IT muppettry.