Canon has issued a warning to EOS-1D X II owners, noting a problem with file corruption that can occur when certain SanDisk CFast cards are used. The issue occurs with the last few images recorded just before the camera is powered off, so Canon's suggested workaround is to capture a number of extra shots when turning the camera off. 

These are the problematic cards named in Canon's advisory: 

The “xxx” at the end of the product number varies depending on the sales region.

  • SanDisk Extreme PRO CFast2.0 64GB (SDCFSP-064G-xxx)
  • SanDisk Extreme PRO CFast2.0 128GB (SDCFSP-128G-xxx)
  • SanDisk Extreme PRO CFast2.0 64GB (SDCFSP-064G-xxxA)
  • SanDisk Extreme PRO CFast2.0 128GB (SDCFSP-128G-xxxA)
  • SanDisk Extreme PRO CFast2.0 64GB (SDCFSP-064G-xxxB)
  • SanDisk Extreme PRO CFast2.0 128GB (SDCFSP-128G-xxxB)

Both Raw and JPEG files are affected, but the number of corrupted images varies according to the compression mode used. When shooting Raw, Canon recommends recording just one extra shot, but shooting small sized JPEGs will require 8 extra shots to protect other images on the card.

The statement makes very clear that the problem is caused by SanDisk's cards, not by the camera. Canon says it may issue a firmware update in early July to address the problem.