A family of Microsoft word processing software products for creating web, email, and print documents.
Jonathan,
Make sure that you send feedback to Microsoft regarding the lost/redefined shortcuts (which is an obvious bug—see previous replies in this thread). Use Help > Feedback from within Word and/or the portal at https://feedbackportal.microsoft.com/feedback/forum/fb6d67e3-301c-ec11-b6e7-0022481f8472.
You should be able to manually modify the shortcut, though. Have you done any troubleshooting to see what fails in that process? For example, are there any signs that your Normal template is being overwritten each time you log in to your PC? If that is what happens, the underlying cause could be a (poorly designed) add-in or, if you are in a corporate environment, it could be company policy (not a very good policy).