See this thread: Internet identity created in new website not working
Internet Identity relies on the WebAuthn standards, which means your biometrics/usb keys are scoped to a single domain by the webbrowser. In above thread are steps to manually transfer them to the other domain.
There isn’t much that can be done about this, it’s a browser design limitation, it adds a lot of security scoping WebAuthn but also adds this complexity when a service like Internet Identity decides to be also available on another domain.
Additionally they can’t deprecate the old domain since it’s needed for legacy services and accounts that are created with the old domain.
TL;DR
Always make a recovery pass phrase backup, so you can get back in, no matter which domain Internet Identity uses. Don’t solely rely on a recovery usb, this doesn’t work on other domain names and is thus useless when a domain is no longer available for some reason.