Firmware Version 1.1.6 for the EOS-1D X Mark II fixes a phenomenon in which the camera may not function normally when images are simultaneously displayed on the camera's LCD monitor and an external monitor (via HDMI output).
For more information and firmware download follow the camera link at:
https://www.canon.co.uk/support/consumer_products/product_ranges/cameras/eos/
For more information and firmware download follow the camera link at:
https://www.canon.co.uk/support/consumer_products/product_ranges/cameras/eos/