Bryan at The-Digital-Picture completed his full review of the Canon RF 100mm f/2.8L IS USM last month, and one of the negative issues that stood out was the focus shift that he experienced with the new RF macro lens.
In the spirit of being thorough, Bryan got himself a second copy of the RF 100mm f/2.8L IS USM Macro to see if he had received a bad copy, or if the shift was by design. It looks like it's the latter.
Did I get a bad copy of the Canon RF 100mm F2.8 L Macro IS USM Lens? My guess was no. Supporting that theory was a technical rep confirming the issue with his lens. The test results shared above have been forwarded to the Canon lens team in Japan. Read the full review
If you only want to read about the focus shift issue and see the tests, just do a search (CTRL-F / CMD-F) for “bad copy” and read what Bryan has discovered with two different copies of the RF 100mm f/2.8L IS USM Macro.
We have been discussing this issue on the Canon Rumors Discord server and one person “Tig“, has been communicating with Bryan about this issue. While he has experienced it, his issues haven't been as pronounced.
… this was at macro scale, at maximum magnification (1.4x), so to have this not move the subject out of the plane of focus at f/4-f/8 means there's very, very little shift. I'd definitely buy the lens again if I knew all this. I tend to shoot it at f/2.8 when running and gunning while hiking, or at something like f/11 – f/14 if doing some table-top macro thing. In both of those cases, you wouldn't be able to notice any shift.
So the issue may not be something all shooters will encounter and it's possible that a firmware update for the RF 100mm f/2.8L IS USM Macro could fix the shift,