Ran into the same problem today (Sequoia 15.0.1, CreateML Version 6.0 Beta (150))
Augmentations were Blur, Crop, Expose, Flip, Rotate
Processed around 12000 images, and 2/3 down it bailed out with the exact error.
I unchecked all the augmentations and Create ML was able to go through the "Extract features..." for all the images. So one image must be broken in such a way that that CVPixel... fails.
But, now CreateML Segfaults instead: Exception Type: EXC_CRASH (SIGABRT)