I thought that the reviewing world had established that this RF 35/1.8 suffers from RSAs - focus shift, and what you're describing seems to fit with this. If so it's a normal characteristic of the lens and you'll have to learn to work around it just like those of us that have RSA effected lenses such as the EF 50/1.2 & Tamron 85/1.8 VC have to.
Very interesting. I had actually missed the focus shift issue in the reviews I had seen on YouTube. The digital picture has a good explanation of it in their review: https://www.the-digital-picture.com/Reviews/Canon-RF-35mm-f-1.8-IS-STM-Macro-Lens.aspx
In my first shoot with the lens I only used f2.0 and f2.5 so that would explain why I wasn’t really experiencing the focus shift issues. It seems most pronounced after 2.8 based on the digital picture review.
How does one compensate for this in real world shooting? I would imagine that adjusting manual focus and bringing the focus point forward would be extremely hit and miss? I’m honestly quite surprised that modern lenses still suffer from this.
It looks like I won’t be using my RF 35 f1.8 at the problem apertures... most likely will keep it at or below f2.5.