A sign-in code that cannot be sent now says so
The sign-in page carried on as if a code had been sent when the email had failed, and asking for another one invalidated the code you already had.
When your sign-in code could not be emailed, the page carried on as if it had been sent and asked you for the code, and you were left waiting for mail that was never coming. It now says the send failed, so you know to try again instead of watching an empty inbox.
Asking for a new code no longer costs you the one you have either. If a resend fails, the code already sitting in your inbox keeps working.