The Canon RF 100mm F2.8 L Macro IS USM Lens Review image quality section has been updated to include the focus shift information provided by Canon's optical engineers.
I'll share the conclusions here:
The response from Canon's optical engineers was to confirm that, due to its 1.4x magnification (1.4:1 reproduction ratio) capability, a magnification far exceeding 1.0x, the RF 100mm F2.8 L Macro IS Lens's optical design exhibits some focus shift.
The focus shift is not sample dependent and is not related to the SA control ring. As focus shift is characteristic of this lens, no production changes to the lens or lens/camera firmware updates are anticipated. Correction, when necessary, is accomplished by focusing slightly in front of the subject.
Read the image quality section of the Canon RF 100mm F2.8 L Macro IS USM Lens Review for the full discussion with samples.