This issue has started suddenly after working for over 6+ months. The registered application is a custom-built internal application that is registered with Azure AD to limit access to only users within the directory. After successful sign in to Microsoft, the Permission requested promptly is displayed and after selecting allow a 'login failed' screen is displayed. The error which is returned to the webserver is a 50000 stating that the token is invalid or the login service is down.
Has anyone else experienced this issue, or have any insight into what would cause this to suddenly occur after no changes were made in the web application or the AD registration settings. Thank you.