Canon will release a firmware update for the EOS-1D X Mark III in early April, as the company communicates through a product advisory:
To Users of EOS-1D X Mark III
Thank you for using Canon products.
We have confirmed that the following phenomenon may occur during use of the EOS 1D X Mark III digital SLR camera. A new firmware release is planned for early April; once the new firmware is ready, we will make an announcement on our website.
We sincerely apologise to users who may have experienced inconvenience due to 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.
Setting procedure: 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.
Please contact your nearest service centre if you have any queries.