Is SmartThings ADT dead? (July 2019) (Lifeshield/Blue by ADT Acquisition and Support comments on EOL)

I had the same issue. The problem is likely a duplicate ControlUnit. If you have two ControlUnits on the ADT Canopy website, you should remove the duplicate. Follow these instructions: ADT Hub System Test Required/Duplicate Sensors/Cellular Module Failure (July 2019)

Once the duplicate ControlUnit is removed, the final step of the Test Mode (conforming connection to monitoring center) will complete.