Known Issue Impacting Duo SMS Passcode Requests (for AT&T and Verizon customers only)
As of 2:21 p.m. on Monday, January 8, the IT Service Desk was made aware of an issue impacting SMS passcode delivery to some AT&T and Verizon customers. Duo Security reported that they are currently investigating the reports and their provider is actively working on resolving the issues. Other Duo authentication methods such as phone calls, Duo Push Notifications, and already generated passcodes are not affected.
We will post any updates as they become available to us.
Story added 8. January 2018, content source with full text you can find at link above.