When running a test on TTS, I tried to send the M2 from the ENABLED state to the STANDBY state. The command failed. I talked to Tiago Ribeiro who confirmed that M2 is stuck in the ENABLED state because it cannot connect to the M2 controller. Here is a print-screen of the command using Jupyter Notebook:

I will add the full traceback from the CSC as a comment later. 

Killing the CSC using ArgoCD was the temporary solution.