There is no issue with focus shift IMO.
I did 10 000s of shots with this fantastic lens and have still not found any problems.
I did a test which You find here:
There is a lot of talk about focus shift of the RF 100L macro. I have used the lens without any issues and have been wondering a long time what's that talk is about.
So I have made four series of pictures with changing aperture.
Subject is a dead hummingbird moth I found and which is pefect for a "real life" test.
I put the camera on a tripod with a macro rail to focus, connected it to my PC. Focus set to manual, IS off.
Electronic shutter and 10s delay to prevent shake. After focussing I didn't touch the camera and set everything via PC.
The focus is set on the eye like in real life by...