Issue reported resolved.
Telephony providers are reporting a fix has been implemented and are monitoring the results.
Our third party telephony provider is reporting delivery issues for SMS that may impact numbers from USA and Canada.
One alternative is to use email OTP: https://www.logintc.com/docs/guides/email-otp/
Another to SMS, users can receive a phone call with an OTP: https://www.logintc.com/docs/guides/phones/#phone-call-otp-authentication
For the LoginTC RADIUS Connector this requires an upgrade to 4.1.0: https://www.logintc.com/docs/connectors/radius/#upgrading