Article 01 covers a single borrower who does not receive a sign-in code. This one covers the other case: several people stop receiving codes at the same time, across different loans and different companies. The handling is different, and so is what you should tell borrowers.
Telling the two apart
One borrower, one phone, everyone else fine — treat it as an account or carrier issue and follow article 01.
Treat it as a platform problem when codes fail for borrowers and staff at once, on more than one loan, within the same short window. In an outage of this kind the code is never sent at all, so checking the phone's spam folder, switching browsers or resetting the password will not help and only costs time.
Check the release notes and service notices page before opening a ticket. Service notices are posted there, and system administrators are notified directly.
Close every browser window before retrying
This is the step people skip. When support makes a change to an account, or when service is restored, the old sign-in session is still holding the failed state, and closing the tab is not enough.
Ask the person to close every open browser window, reopen the browser, and sign in again. Several people reported "still not working" after a fix was already in place, purely because an old window was still open.
MFA may be switched off while an outage runs
If codes cannot be delivered, multi-factor authentication can be turned off at account level as a temporary measure, and sign-in then works with email and password alone. Someone who signs in with no code prompt during an outage is not seeing a bug.
MFA is turned back on once delivery is restored, account by account, and the code prompt returns at the next sign-in. Nothing needs doing in advance.
If you still need to raise it
File one ticket listing everyone affected rather than one per person, and include the email address on each account. Simultaneous failures are almost always a provider incident, and one consolidated ticket lets support correlate them faster.