Canon has made Canon EOS-1D X Mark III
firmware update version 1.2.1 available for
Firmware Version 1.2.1 incorporates the following fixes and enhancements:
- Fixes a phenomenon, in which, after updating the camera’s firmware to version 1.2.0, the Smart Controller may respond slowly or not at all on some cameras. The phenomenon described above may occur in cameras whose first two digits of the serial number are "01" "02" "03" or "04".