Thank you for using Canon products.
We have confirmed that the following phenomenon occurs during use of the EOS-1D X Mark III digital SLR camera. Once the preparations for the new firmware are complete, we will make an announcement on our website.
We would like to offer our sincere apologies to users of these products who have been inconvenienced by this issue.
When the camera is used with the electronic level set to “Show” in the viewfinder display, in rare cases, the camera may not perform normally when operating the AF-ON button or shutter button.
EOS-1D X Mark III (Firmware version 1.0.0)
Use the “Hide” setting for the electronic level in the viewfinder display.
Menu / Set-up 2 tab / Viewfinder display / Electronic level [Hide]
*Default setting: [Hide]
In early-April 2020, we plan to release a firmware update to address the phenomenon listed above.