I was using my Canon EOS R6 with the RONIN-S just fine (both on the latest current firmware as of 2021.11.25), in July I was using the MCC cable to connect the Ronin to my camera to control the record button, but more importantly to activate ActiveTrack on my phone mounted on top of the camera.

This suddenly stopped working. I purchased two extra MCC cables, but neither of them worked. Is it possible that the MCC port is malfunctioning? The camera's USB port is working as I have tested it.

Hi Mikkel, sorry to read about the issue. Would you mind providing a video for further confirmation? If the connection port is damaged, you may need to send it back for further service. You can start a case at link: https://www.dji.com/us/service/repair
We will do our best to help this out.